Chapter 22. The INFORMATION_SCHEMA Database

Table of Contents

22.1. The INFORMATION_SCHEMA SCHEMATA Table
22.2. The INFORMATION_SCHEMA TABLES Table
22.3. The INFORMATION_SCHEMA COLUMNS Table
22.4. The INFORMATION_SCHEMA STATISTICS Table
22.5. The INFORMATION_SCHEMA USER_PRIVILEGES Table
22.6. The INFORMATION_SCHEMA SCHEMA_PRIVILEGES Table
22.7. The INFORMATION_SCHEMA TABLE_PRIVILEGES Table
22.8. The INFORMATION_SCHEMA COLUMN_PRIVILEGES Table
22.9. The INFORMATION_SCHEMA CHARACTER_SETS Table
22.10. The INFORMATION_SCHEMA COLLATIONS Table
22.11. The INFORMATION_SCHEMA COLLATION_CHARACTER_SET_APPLICABILITY Table
22.12. The INFORMATION_SCHEMA TABLE_CONSTRAINTS Table
22.13. The INFORMATION_SCHEMA KEY_COLUMN_USAGE Table
22.14. The INFORMATION_SCHEMA ROUTINES Table
22.15. The INFORMATION_SCHEMA VIEWS Table
22.16. The INFORMATION_SCHEMA TRIGGERS Table
22.17. The INFORMATION_SCHEMA PLUGINS Table
22.18. The INFORMATION_SCHEMA ENGINES Table
22.19. The INFORMATION_SCHEMA PARTITIONS Table
22.20. The INFORMATION_SCHEMA EVENTS Table
22.21. The INFORMATION_SCHEMA FILES Table
22.22. The INFORMATION_SCHEMA PROCESSLIST Table
22.23. The INFORMATION_SCHEMA REFERENTIAL_CONSTRAINTS Table
22.24. The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables
22.25. The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables
22.26. Other INFORMATION_SCHEMA Tables
22.27. Extensions to SHOW Statements

INFORMATION_SCHEMA provides access to database metadata.

Metadata is data about the data, such as the name of a database or table, the data type of a column, or access privileges. Other terms that sometimes are used for this information are data dictionary and system catalog.

INFORMATION_SCHEMA is the information database, the place that stores information about all the other databases that the MySQL server maintains. Inside INFORMATION_SCHEMA there are several read-only tables. They are actually views, not base tables, so there are no files associated with them.

In effect, we have a database named INFORMATION_SCHEMA, although the server does not create a database directory with that name. It is possible to select INFORMATION_SCHEMA as the default database with a USE statement, but it is possible only to read the contents of tables. You cannot insert into them, update them, or delete from them.

Here is an example of a statement that retrieves information from INFORMATION_SCHEMA:

mysql> SELECT table_name, table_type, engine
    -> FROM information_schema.tables
    -> WHERE table_schema = 'db5'
    -> ORDER BY table_name DESC;
+------------+------------+--------+
| table_name | table_type | engine |
+------------+------------+--------+
| v56        | VIEW       | NULL   |
| v3         | VIEW       | NULL   |
| v2         | VIEW       | NULL   |
| v          | VIEW       | NULL   |
| tables     | BASE TABLE | MyISAM |
| t7         | BASE TABLE | MyISAM |
| t3         | BASE TABLE | MyISAM |
| t2         | BASE TABLE | MyISAM |
| t          | BASE TABLE | MyISAM |
| pk         | BASE TABLE | InnoDB |
| loop       | BASE TABLE | MyISAM |
| kurs       | BASE TABLE | MyISAM |
| k          | BASE TABLE | MyISAM |
| into       | BASE TABLE | MyISAM |
| goto       | BASE TABLE | MyISAM |
| fk2        | BASE TABLE | InnoDB |
| fk         | BASE TABLE | InnoDB |
+------------+------------+--------+
17 rows in set (0.01 sec)

Explanation: The statement requests a list of all the tables in database db5, in reverse alphabetical order, showing just three pieces of information: the name of the table, its type, and its storage engine.

Each MySQL user has the right to access these tables, but can see only the rows in the tables that correspond to objects for which the user has the proper access privileges. In some cases (for example, the ROUTINE_DEFINITION column in the INFORMATION_SCHEMA.ROUTINES table), users who have insufficient privileges will see NULL.

The SELECT ... FROM INFORMATION_SCHEMA statement is intended as a more consistent way to provide access to the information provided by the various SHOW statements that MySQL supports (SHOW DATABASES, SHOW TABLES, and so forth). Using SELECT has these advantages, compared to SHOW:

However, because SHOW is popular with MySQL employees and users, and because it might be confusing were it to disappear, the advantages of conventional syntax are not a sufficient reason to eliminate SHOW. In fact, along with the implementation of INFORMATION_SCHEMA, there are enhancements to SHOW as well. These are described in Section 22.27, “Extensions to SHOW Statements”.

There is no difference between the privileges required for SHOW statements and those required to select information from INFORMATION_SCHEMA. In either case, you have to have some privilege on an object in order to see information about it.

The implementation for the INFORMATION_SCHEMA table structures in MySQL follows the ANSI/ISO SQL:2003 standard Part 11 Schemata. Our intent is approximate compliance with SQL:2003 core feature F021 Basic information schema.

Users of SQL Server 2000 (which also follows the standard) may notice a strong similarity. However, MySQL has omitted many columns that are not relevant for our implementation, and added columns that are MySQL-specific. One such column is the ENGINE column in the INFORMATION_SCHEMA.TABLES table.

Although other DBMSs use a variety of names, like syscat or system, the standard name is INFORMATION_SCHEMA.

The following sections describe each of the tables and columns that are in INFORMATION_SCHEMA. For each column, there are three pieces of information:

To avoid using any name that is reserved in the standard or in DB2, SQL Server, or Oracle, we changed the names of some columns marked “MySQL extension”. (For example, we changed COLLATION to TABLE_COLLATION in the TABLES table.) See the list of reserved words near the end of this article: http://www.dbazine.com/gulutzan5.shtml.

The definition for character columns (for example, TABLES.TABLE_NAME) is generally VARCHAR(N) CHARACTER SET utf8 where N is at least 64.

Each section indicates what SHOW statement is equivalent to a SELECT that retrieves information from INFORMATION_SCHEMA, if there is such a statement.

Note: At present, there are some missing columns and some columns out of order. We are working on this and updating the documentation as changes are made.

For answers to questions that are often asked concerning the INFORMATION_SCHEMA database, see Section A.8, “MySQL 5.0 FAQ — INFORMATION_SCHEMA.

22.1. The INFORMATION_SCHEMA SCHEMATA Table

A schema is a database, so the SCHEMATA table provides information about databases.

INFORMATION_SCHEMA NameSHOW NameRemarks
CATALOG_NAME NULL
SCHEMA_NAME Database
DEFAULT_CHARACTER_SET_NAME  
DEFAULT_COLLATION_NAME  
SQL_PATH NULL

The following statements are equivalent:

SELECT SCHEMA_NAME AS `Database`
  FROM INFORMATION_SCHEMA.SCHEMATA
  [WHERE SCHEMA_NAME LIKE 'wild']

SHOW DATABASES
  [LIKE 'wild']

22.2. The INFORMATION_SCHEMA TABLES Table

The TABLES table provides information about tables in databases.

INFORMATION_SCHEMA NameSHOW NameRemarks
TABLE_CATALOG NULL
TABLE_SCHEMATable_... 
TABLE_NAMETable_... 
TABLE_TYPE  
ENGINEEngineMySQL extension
VERSIONVersionMySQL extension
ROW_FORMATRow_formatMySQL extension
TABLE_ROWSRowsMySQL extension
AVG_ROW_LENGTHAvg_row_lengthMySQL extension
DATA_LENGTHData_lengthMySQL extension
MAX_DATA_LENGTHMax_data_lengthMySQL extension
INDEX_LENGTHIndex_lengthMySQL extension
DATA_FREEData_freeMySQL extension
AUTO_INCREMENTAuto_incrementMySQL extension
CREATE_TIMECreate_timeMySQL extension
UPDATE_TIMEUpdate_timeMySQL extension
CHECK_TIMECheck_timeMySQL extension
TABLE_COLLATIONCollationMySQL extension
CHECKSUMChecksumMySQL extension
CREATE_OPTIONSCreate_optionsMySQL extension
TABLE_COMMENTCommentMySQL extension

Notes:

  • TABLE_SCHEMA and TABLE_NAME are a single field in a SHOW display, for example Table_in_db1.

  • TABLE_TYPE should be BASE TABLE or VIEW. If table is temporary, then TABLE_TYPE = TEMPORARY. (There are no temporary views, so this is not ambiguous.)

  • For partitioned tables, beginning with MySQL 5.1.9, the ENGINE column shows the name of the storage engine used by all partitions. (Previously, this column showed PARTITION for such tables.)

  • The TABLE_ROWS column is NULL if the table is in the INFORMATION_SCHEMA database. For InnoDB tables, the row count is only a rough estimate used in SQL optimization.

  • For tables using the NDBCLUSTER storage engine, beginning with MySQL 5.1.12, the DATA_LENGTH column reflects the true amount of storage for variable-width columns. (See Bug#18413.)

    Note: Because MySQL Cluster allocates storage for variable-width columns in 10-page extents of 32 kilobytes each, space usage for such columns is reported in increments of 320 KB.

  • We have nothing for the table's default character set. TABLE_COLLATION is close, because collation names begin with a character set name.

  • Beginning with MySQL 5.1.9, the CREATE_OPTIONS column shows partitioned if the table is partitioned.

The following statements are equivalent:

SELECT table_name FROM INFORMATION_SCHEMA.TABLES
  [WHERE table_schema = 'db_name']
  [WHERE|AND table_name LIKE 'wild']

SHOW TABLES
  [FROM db_name]
  [LIKE 'wild']

22.3. The INFORMATION_SCHEMA COLUMNS Table

The COLUMNS table provides information about columns in tables.

INFORMATION_SCHEMA NameSHOW NameRemarks
TABLE_CATALOG NULL
TABLE_SCHEMA  
TABLE_NAME  
COLUMN_NAMEField 
ORDINAL_POSITION see notes
COLUMN_DEFAULTDefault 
IS_NULLABLENull 
DATA_TYPEType 
CHARACTER_MAXIMUM_LENGTHType 
CHARACTER_OCTET_LENGTH  
NUMERIC_PRECISIONType 
NUMERIC_SCALEType 
CHARACTER_SET_NAME  
COLLATION_NAMECollation 
COLUMN_TYPETypeMySQL extension
COLUMN_KEYKeyMySQL extension
EXTRAExtraMySQL extension
COLUMN_COMMENTCommentMySQL extension

Notes:

  • In SHOW, the Type display includes values from several different COLUMNS columns.

  • ORDINAL_POSITION is necessary because you might want to say ORDER BY ORDINAL_POSITION. Unlike SHOW, SELECT does not have automatic ordering.

  • CHARACTER_OCTET_LENGTH should be the same as CHARACTER_MAXIMUM_LENGTH, except for multi-byte character sets.

  • CHARACTER_SET_NAME can be derived from Collation. For example, if you say SHOW FULL COLUMNS FROM t, and you see in the Collation column a value of latin1_swedish_ci, the character set is what's before the first underscore: latin1.

The following statements are nearly equivalent:

SELECT COLUMN_NAME, DATA_TYPE, IS_NULLABLE, COLUMN_DEFAULT
  FROM INFORMATION_SCHEMA.COLUMNS
  WHERE table_name = 'tbl_name'
  [AND table_schema = 'db_name']
  [AND column_name LIKE 'wild']

SHOW COLUMNS
  FROM tbl_name
  [FROM db_name]
  [LIKE 'wild']

22.4. The INFORMATION_SCHEMA STATISTICS Table

The STATISTICS table provides information about table indexes.

INFORMATION_SCHEMA NameSHOW NameRemarks
TABLE_CATALOG NULL
TABLE_SCHEMA = Database
TABLE_NAMETable 
NON_UNIQUENon_unique 
INDEX_SCHEMA = Database
INDEX_NAMEKey_name 
SEQ_IN_INDEXSeq_in_index 
COLUMN_NAMEColumn_name 
COLLATIONCollation 
CARDINALITYCardinality 
SUB_PARTSub_partMySQL extension
PACKEDPackedMySQL extension
NULLABLENullMySQL extension
INDEX_TYPEIndex_typeMySQL extension
COMMENTCommentMySQL extension

Notes:

  • There is no standard table for indexes. The preceding list is similar to what SQL Server 2000 returns for sp_statistics, except that we replaced the name QUALIFIER with CATALOG and we replaced the name OWNER with SCHEMA.

    Clearly, the preceding table and the output from SHOW INDEX are derived from the same parent. So the correlation is already close.

The following statements are equivalent:

SELECT * FROM INFORMATION_SCHEMA.STATISTICS
  WHERE table_name = 'tbl_name'
  [AND table_schema = 'db_name']

SHOW INDEX
  FROM tbl_name
  [FROM db_name]

22.5. The INFORMATION_SCHEMA USER_PRIVILEGES Table

The USER_PRIVILEGES table provides information about global privileges. This information comes from the mysql.user grant table.

INFORMATION_SCHEMA NameSHOW NameRemarks
GRANTEE 'user_name'@'host_name' value, MySQL extension
TABLE_CATALOG NULL, MySQL extension
PRIVILEGE_TYPE MySQL extension
IS_GRANTABLE MySQL extension

Notes:

  • This is a non-standard table. It takes its values from the mysql.user table.

22.6. The INFORMATION_SCHEMA SCHEMA_PRIVILEGES Table

The SCHEMA_PRIVILEGES table provides information about schema (database) privileges. This information comes from the mysql.db grant table.

INFORMATION_SCHEMA NameSHOW NameRemarks
GRANTEE 'user_name'@'host_name' value, MySQL extension
TABLE_CATALOG NULL, MySQL extension
TABLE_SCHEMA MySQL extension
PRIVILEGE_TYPE MySQL extension
IS_GRANTABLE MySQL extension

Notes:

  • This is a non-standard table. It takes its values from the mysql.db table.

22.7. The INFORMATION_SCHEMA TABLE_PRIVILEGES Table

The TABLE_PRIVILEGES table provides information about table privileges. This information comes from the mysql.tables_priv grant table.

INFORMATION_SCHEMA NameSHOW NameRemarks
GRANTEE 'user_name'@'host_name' value
TABLE_CATALOG NULL
TABLE_SCHEMA  
TABLE_NAME  
PRIVILEGE_TYPE  
IS_GRANTABLE  

Notes:

  • PRIVILEGE_TYPE can contain one (and only one) of these values: SELECT, INSERT, UPDATE, REFERENCES, ALTER, INDEX, DROP, CREATE VIEW.

The following statements are not equivalent:

SELECT ... FROM INFORMATION_SCHEMA.TABLE_PRIVILEGES

SHOW GRANTS ...

22.8. The INFORMATION_SCHEMA COLUMN_PRIVILEGES Table

The COLUMN_PRIVILEGES table provides information about column privileges. This information comes from the mysql.columns_priv grant table.

INFORMATION_SCHEMA NameSHOW NameRemarks
GRANTEE 'user_name'@'host_name' value
TABLE_CATALOG NULL
TABLE_SCHEMA  
TABLE_NAME  
COLUMN_NAME  
PRIVILEGE_TYPE  
IS_GRANTABLE  

Notes:

  • In the output from SHOW FULL COLUMNS, the privileges are all in one field and in lowercase, for example, select,insert,update,references. In COLUMN_PRIVILEGES, there is one privilege per row, in uppercase.

  • PRIVILEGE_TYPE can contain one (and only one) of these values: SELECT, INSERT, UPDATE, REFERENCES.

  • If the user has GRANT OPTION privilege, IS_GRANTABLE should be YES. Otherwise, IS_GRANTABLE should be NO. The output does not list GRANT OPTION as a separate privilege.

The following statements are not equivalent:

SELECT ... FROM INFORMATION_SCHEMA.COLUMN_PRIVILEGES

SHOW GRANTS ...

22.9. The INFORMATION_SCHEMA CHARACTER_SETS Table

The CHARACTER_SETS table provides information about available character sets.

INFORMATION_SCHEMA NameSHOW NameRemarks
CHARACTER_SET_NAMECharset 
DEFAULT_COLLATE_NAMEDefault collation 
DESCRIPIONDescriptionMySQL extension
MAXLENMaxlenMySQL extension

The following statements are equivalent:

SELECT * FROM INFORMATION_SCHEMA.CHARACTER_SETS
  [WHERE name LIKE 'wild']

SHOW CHARACTER SET
  [LIKE 'wild']

22.10. The INFORMATION_SCHEMA COLLATIONS Table

The COLLATIONS table provides information about collations for each character set.

INFORMATION_SCHEMA NameSHOW NameRemarks
COLLATION_NAMECollation 
CHARACTER_SET_NAMECharsetMySQL extension
IDIdMySQL extension
IS_DEFAULTDefaultMySQL extension
IS_COMPILEDCompiledMySQL extension
SORTLENSortlenMySQL extension

The following statements are equivalent:

SELECT COLLATION_NAME FROM INFORMATION_SCHEMA.COLLATIONS
  [WHERE collation_name LIKE 'wild']

SHOW COLLATION
  [LIKE 'wild']

22.11. The INFORMATION_SCHEMA COLLATION_CHARACTER_SET_APPLICABILITY Table

The COLLATION_CHARACTER_SET_APPLICABILITY table indicates what character set is applicable for what collation. The columns are equivalent to the first two display fields that we get from SHOW COLLATION.

INFORMATION_SCHEMA NameSHOW NameRemarks
COLLATION_NAMECollation 
CHARACTER_SET_NAMECharset 

22.12. The INFORMATION_SCHEMA TABLE_CONSTRAINTS Table

The TABLE_CONSTRAINTS table describes which tables have constraints.

INFORMATION_SCHEMA NameSHOW NameRemarks
CONSTRAINT_CATALOG NULL
CONSTRAINT_SCHEMA  
CONSTRAINT_NAME  
TABLE_SCHEMA  
TABLE_NAME  
CONSTRAINT_TYPE  

Notes:

  • The CONSTRAINT_TYPE value can be UNIQUE, PRIMARY KEY, or FOREIGN KEY.

  • The UNIQUE and PRIMARY KEY information is about the same as what you get from the Key_name field in the output from SHOW INDEX when the Non_unique field is 0.

  • The CONSTRAINT_TYPE column can contain one of these values: UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK. This is a CHAR (not ENUM) column. The CHECK value is not available until we support CHECK.

22.13. The INFORMATION_SCHEMA KEY_COLUMN_USAGE Table

The KEY_COLUMN_USAGE table describes which key columns have constraints.

INFORMATION_SCHEMA NameSHOW NameRemarks
CONSTRAINT_CATALOG NULL
CONSTRAINT_SCHEMA  
CONSTRAINT_NAME  
TABLE_CATALOG  
TABLE_SCHEMA  
TABLE_NAME  
COLUMN_NAME  
ORDINAL_POSITION  
POSITION_IN_UNIQUE_CONSTRAINT  
REFERENCED_TABLE_SCHEMA  
REFERENCED_TABLE_NAME  
REFERENCED_COLUMN_NAME  

Notes:

  • If the constraint is a foreign key, then this is the column of the foreign key, not the column that the foreign key references.

  • The value of ORDINAL_POSITION is the column's position within the constraint, not the column's position within the table. Column positions are numbered beginning with 1.

  • The value of POSITION_IN_UNIQUE_CONSTRAINT is NULL for unique and primary-key constraints. For foreign-key constraints, it is the ordinal position in key of the table that is being referenced.

    For example, suppose that there are two tables name t1 and t3 that have the following definitions:

    CREATE TABLE t1
    (
        s1 INT,
        s2 INT,
        s3 INT,
        PRIMARY KEY(s3)
    ) ENGINE=InnoDB;
    
    CREATE TABLE t3
    (
        s1 INT,
        s2 INT,
        s3 INT,
        KEY(s1),
        CONSTRAINT CO FOREIGN KEY (s2) REFERENCES t1(s3)
    ) ENGINE=InnoDB;
    

    For those two tables, the KEY_COLUMN_USAGE table has two rows:

    • One row with CONSTRAINT_NAME = 'PRIMARY', TABLE_NAME = 't1', COLUMN_NAME = 's3', ORDINAL_POSITION = 1, POSITION_IN_UNIQUE_CONSTRAINT = NULL.

    • One row with CONSTRAINT_NAME = 'CO', TABLE_NAME = 't3', COLUMN_NAME = 's2', ORDINAL_POSITION = 1, POSITION_IN_UNIQUE_CONSTRAINT = 1.

22.14. The INFORMATION_SCHEMA ROUTINES Table

The ROUTINES table provides information about stored routines (both procedures and functions). The ROUTINES table does not include user-defined functions (UDFs) at this time.

The column named “mysql.proc name” indicates the mysql.proc table column that corresponds to the INFORMATION_SCHEMA.ROUTINES table column, if any.

INFORMATION_SCHEMA Namemysql.proc NameRemarks
SPECIFIC_NAMEspecific_name 
ROUTINE_CATALOG NULL
ROUTINE_SCHEMAdb 
ROUTINE_NAMEname 
ROUTINE_TYPEtype{PROCEDURE|FUNCTION}
DTD_IDENTIFIER (data type descriptor)
ROUTINE_BODY SQL
ROUTINE_DEFINITIONbody 
EXTERNAL_NAME NULL
EXTERNAL_LANGUAGElanguageNULL
PARAMETER_STYLE SQL
IS_DETERMINISTICis_deterministic 
SQL_DATA_ACCESSsql_data_access 
SQL_PATH NULL
SECURITY_TYPEsecurity_type 
CREATEDcreated 
LAST_ALTEREDmodified 
SQL_MODEsql_modeMySQL extension
ROUTINE_COMMENTcommentMySQL extension
DEFINERdefinerMySQL extension

Notes:

  • MySQL calculates EXTERNAL_LANGUAGE thus:

    • If mysql.proc.language='SQL', EXTERNAL_LANGUAGE is NULL

    • Otherwise, EXTERNAL_LANGUAGE is what is in mysql.proc.language. However, we do not have external languages yet, so it is always NULL.

22.15. The INFORMATION_SCHEMA VIEWS Table

The VIEWS table provides information about views in databases. You must have the SHOW VIEW privilege to access this table.

INFORMATION_SCHEMA NameSHOW NameRemarks
TABLE_CATALOG NULL
TABLE_SCHEMA  
TABLE_NAME  
VIEW_DEFINITION  
CHECK_OPTION  
IS_UPDATABLE  
DEFINER  
SECURITY_TYPE  

Notes:

  • The VIEW_DEFINITION column has most of what you see in the Create Table field that SHOW CREATE VIEW produces. Skip the words before SELECT and skip the words WITH CHECK OPTION. Suppose that the original statement was:

    CREATE VIEW v AS
      SELECT s2,s1 FROM t
      WHERE s1 > 5
      ORDER BY s1
      WITH CHECK OPTION;
    

    Then the view definition looks like this:

    SELECT s2,s1 FROM t WHERE s1 > 5 ORDER BY s1
    
  • The CHECK_OPTION column always has a value of NONE.

  • The IS_UPDATABLE column is YES if the view is updatable, NO if the view is not updatable.

  • The DEFINER column indicates who defined the view. SECURITY_TYPE has a value of DEFINER or INVOKER.

22.16. The INFORMATION_SCHEMA TRIGGERS Table

The TRIGGERS table provides information about triggers. You must have the SUPER privilege to access this table.

INFORMATION_SCHEMA NameSHOW NameRemarks
TRIGGER_CATALOG NULL
TRIGGER_SCHEMA  
TRIGGER_NAMETrigger 
EVENT_MANIPULATIONEvent 
EVENT_OBJECT_CATALOG NULL
EVENT_OBJECT_SCHEMA  
EVENT_OBJECT_TABLETable 
ACTION_ORDER 0
ACTION_CONDITION NULL
ACTION_STATEMENTStatement 
ACTION_ORIENTATION ROW
ACTION_TIMINGTiming 
ACTION_REFERENCE_OLD_TABLE NULL
ACTION_REFERENCE_NEW_TABLE NULL
ACTION_REFERENCE_OLD_ROW OLD
ACTION_REFERENCE_NEW_ROW NEW
CREATED NULL (0)
SQL_MODE MySQL extension
DEFINER MySQL extension

Notes:

  • The TRIGGER_SCHEMA and TRIGGER_NAME columns contain the name of the database in which the trigger occurs and the trigger name, respectively.

  • The EVENT_MANIPULATION column contains one of the values 'INSERT', 'DELETE', or 'UPDATE'.

  • As noted in Chapter 19, Triggers, every trigger is associated with exactly one table. The EVENT_OBJECT_SCHEMA and EVENT_OBJECT_TABLE columns contain the database in which this table occurs, and the table's name.

  • The ACTION_ORDER statement contains the ordinal position of the trigger's action within the list of all similar triggers on the same table. Currently, this value is always 0, because it is not possible to have more than one trigger with the same EVENT_MANIPULATION and ACTION_TIMING on the same table.

  • The ACTION_STATEMENT column contains the statement to be executed when the trigger is invoked. This is the same as the text displayed in the Statement column of the output from SHOW TRIGGERS. Note that this text uses UTF-8 encoding.

  • The ACTION_ORIENTATION column always contains the value 'ROW'.

  • The ACTION_TIMING column contains one of the two values 'BEFORE' or 'AFTER'.

  • The columns ACTION_REFERENCE_OLD_ROW and ACTION_REFERENCE_NEW_ROW contain the old and new column identifiers, respectively. This means that ACTION_REFERENCE_OLD_ROW always contains the value 'OLD' and ACTION_REFERENCE_NEW_ROW always contains the value 'NEW'.

  • The SQL_MODE column shows the server SQL mode that was in effect at the time when the trigger was created (and thus which remains in effect for this trigger whenever it is invoked, regardless of the current server SQL mode). The possible range of values for this column is the same as that of the sql_mode system variable. See Section 5.2.6, “SQL Modes”.

  • The DEFINER column was added in MySQL 5.1.2. DEFINER indicates who defined the trigger.

  • The following columns currently always contain NULL: TRIGGER_CATALOG, EVENT_OBJECT_CATALOG, ACTION_CONDITION, ACTION_REFERENCE_OLD_TABLE, ACTION_REFERENCE_NEW_TABLE, and CREATED.

Example, using the ins_sum trigger defined in Section 19.3, “Using Triggers”:

mysql> SELECT * FROM INFORMATION_SCHEMA.TRIGGERS\G
*************************** 1. row ***************************
           TRIGGER_CATALOG: NULL
            TRIGGER_SCHEMA: test
              TRIGGER_NAME: ins_sum
        EVENT_MANIPULATION: INSERT
      EVENT_OBJECT_CATALOG: NULL
       EVENT_OBJECT_SCHEMA: test
        EVENT_OBJECT_TABLE: account
              ACTION_ORDER: 0
          ACTION_CONDITION: NULL
          ACTION_STATEMENT: SET @sum = @sum + NEW.amount
        ACTION_ORIENTATION: ROW
             ACTION_TIMING: BEFORE
ACTION_REFERENCE_OLD_TABLE: NULL
ACTION_REFERENCE_NEW_TABLE: NULL
  ACTION_REFERENCE_OLD_ROW: OLD
  ACTION_REFERENCE_NEW_ROW: NEW
                   CREATED: NULL
                  SQL_MODE:
                   DEFINER: me@localhost

See also Section 13.5.4.29, “SHOW TRIGGERS Syntax”.

22.17. The INFORMATION_SCHEMA PLUGINS Table

The PLUGINS table provides information about server plugins.

INFORMATION_SCHEMA NameSHOW NameRemarks
PLUGIN_NAMENameMySQL extension
PLUGIN_VERSION MySQL extension
PLUGIN_STATUSStatusMySQL extension
PLUGIN_TYPETypeMySQL extension
PLUGIN_TYPE_VERSION MySQL extension
PLUGIN_LIBRARYLibraryMySQL extension
PLUGIN_LIBRARY_VERSION MySQL extension
PLUGIN_AUTHOR MySQL extension
PLUGIN_DESCRIPTION MySQL extension

Notes:

  • The PLUGINS table is a non-standard table. It was added in MySQL 5.1.5.

See also Section 13.5.4.20, “SHOW PLUGINS Syntax”.

22.18. The INFORMATION_SCHEMA ENGINES Table

The PLUGINS table provides information about storage engines.

INFORMATION_SCHEMA NameSHOW NameRemarks
ENGINEEngineMySQL extension
SUPPORTSupportMySQL extension
COMMENTCommentMySQL extension
TRANSACTIONSTransactionsMySQL extension
XAXAMySQL extension
SAVEPOINTSSavepointsMySQL extension

Notes:

  • The ENGINES table is a non-standard table. It was added in MySQL 5.1.5.

See also Section 13.5.4.13, “SHOW ENGINES Syntax”.

22.19. The INFORMATION_SCHEMA PARTITIONS Table

The PARTITIONS table provides information about table partitions. See Chapter 16, Partitioning, for more information about partitioning tables.

INFORMATION_SCHEMA NameSHOW NameRemarks
TABLE_CATALOG MySQL extension
TABLE_SCHEMA MySQL extension
TABLE_NAME MySQL extension
PARTITION_NAME MySQL extension
SUBPARTITION_NAME MySQL extension
PARTITION_ORDINAL_POSITION MySQL extension
SUBPARTITION_ORDINAL_POSITION MySQL extension
PARTITION_METHOD MySQL extension
SUBPARTITION_METHOD MySQL extension
PARTITION_EXPRESSION MySQL extension
SUBPARTITION_EXPRESSION MySQL extension
PARTITION_DESCRIPTION MySQL extension
TABLE_ROWS MySQL extension
AVG_ROW_LENGTH MySQL extension
DATA_LENGTH MySQL extension
MAX_DATA_LENGTH MySQL extension
INDEX_LENGTH MySQL extension
DATA_FREE MySQL extension
CREATE_TIME MySQL extension
UPDATE_TIME MySQL extension
CHECK_TIME MySQL extension
CHECKSUM MySQL extension
PARTITION_COMMENT MySQL extension
NODEGROUP MySQL extension
TABLESPACE_NAME MySQL extension

Notes:

  • The PARTITIONS table is a non-standard table. It was added in MySQL 5.1.6.

    Each record in this table corresponds to an individual partition or subpartition of a partitioned table.

  • TABLE_CATALOG: This column is always NULL.

  • TABLE_SCHEMA: This column contains the name of the database to which the table belongs.

  • TABLE_NAME: This column contains the name of the table containing the partition.

  • PARTITION_NAME: The name of the partition.

  • SUBPARTITION_NAME: If the PARTITIONS table record represents a subpartition, then this column contains the name of subpartition; otherwise it is NULL.

  • PARTITION_ORDINAL_POSITION: All partitions are indexed in the same order as they are defined, with 1 being the number assigned to the first partition. The indexing can change as partitions are added, dropped, and reorganized; the number shown is this column reflects the current order, taking into account any indexing changes.

  • SUBPARTITION_ORDINAL_POSITION: Subpartitions within a given partition are also indexed and reindexed in the same manner as partitions are indexed within a table.

  • PARTITION_METHOD: One of the values RANGE, LIST, HASH, LINEAR HASH, KEY, or LINEAR KEY; that is, one of the available partitioning types as discussed in Section 16.2, “Partition Types”.

  • SUBPARTITION_METHOD: One of the values HASH, LINEAR HASH, KEY, or LINEAR KEY; that is, one of the available subpartitioning types as discussed in Section 16.2.5, “Subpartitioning”.

  • PARTITION_EXPRESSION: This is the expression for the partitioning function used in the CREATE TABLE or ALTER TABLE statement that created the table's current partitioning scheme.

    For example, consider a partitioned table created in the test database using this statement:

    CREATE TABLE tp (
        c1 INT,
        c2 INT,
        c3 VARCHAR(25) 
    )
    PARTITION BY HASH(c1 + c2)
    PARTITIONS 4;
    

    The PARTITION_EXPRESSION column in a PARTITIONS table record for a partition from this table displays c1 + c2, as shown here:

    mysql> SELECT DISTINCT PARTITION_EXPRESSION 
         >     FROM INFORMATION_SCHEMA.PARTITIONS
         >     WHERE TABLE_NAME='tp' AND TABLE_SCHEMA='test';
    +----------------------+
    | PARTITION_EXPRESSION |
    +----------------------+
    | c1 + c2              |
    +----------------------+
    1 row in set (0.09 sec)
    
  • SUBPARTITION_EXPRESSION: This works in the same fashion for the subpartitioning expression that defines the subpartitioning for a table as PARTITION_EXPRESSION does for the partitioning expression used to define a table's partitioning.

    If the table has no subpartitions, then this column is NULL.

  • PARTITION_DESCRIPTION: This column is used for RANGE and LIST partitions. For a RANGE partition, it contains the value set in the partition's VALUES LESS THAN clause, which can be either an integer or MAXVALUE. For a LIST partition, this column contains the values defined in the partition's VALUES IN clause, which is a comma-separated list of integer values.

    For partitions whose PARTITION_METHOD is other than RANGE or LIST, this column is always NULL.

  • TABLE_ROWS: The number of table rows in the partition.

  • AVG_ROW_LENGTH: The average length of the rows stored in this partition or subpartition, in bytes.

    This is the same as DATA_LENGTH divided by TABLE_ROWS.

  • DATA_LENGTH: The total length of all rows stored in this partition or subpartition, in bytes — that is, the total number of bytes stored in the partition or subpartition.

  • MAX_DATA_LENGTH: The maximum number of bytes that can be stored in this partition or subpartition.

  • INDEX_LENGTH: The length of the index file for this partition or subpartition, in bytes.

  • DATA_FREE: The number of bytes allocated to the partition or subpartition but not used.

  • CREATE_TIME: The time of the partition's or subpartition's creation.

  • UPDATE_TIME: The time that the partition or subpartition was last modified.

  • CHECK_TIME: The last time that the table to which this partition or subpartition belongs was checked.

    Note: Some storage engines do not update this time; for tables using these storage engines, this value is always NULL.

  • CHECKSUM: The checksum value, if any; otherwise, this column is NULL.

  • PARTITION_COMMENT: This column contains the text of any comment made for the partition.

    The default value for this column is an empty string.

  • NODEGROUP: This is the nodegroup to which the partition belongs. This is relevant only to MySQL Cluster tables; otherwise the value of this column is always 0.

  • TABLESPACE_NAME: This column contains the name of tablespace to which the partition belongs. In MySQL 5.1, the value of this column is always DEFAULT.

  • Important: If any partitioned tables created in a MySQL version prior to MySQL 5.1.6 are present following an upgrade to MySQL 5.1.6 or later, it is not possible to SELECT from, SHOW, or DESCRIBE the PARTITIONS table. See Section E.1.10, “Changes in release 5.1.6 (01 February 2006)” before upgrading from MySQL 5.1.5 or earlier to MySQL 5.1.6 or later.

  • A non-partitioned table has one record in INFORMATION_SCHEMA.PARTITIONS; however, the values of the PARTITION_NAME, SUBPARTITION_NAME, PARTITION_ORDINAL_POSITION, SUBPARTITION_ORDINAL_POSITION, PARTITION_METHOD, SUBPARTITION_METHOD, PARTITION_EXPRESSION, SUBPARTITION_EXPRESSION, and PARTITION_DESCRIPTION columns are all NULL. (The PARTITION_COMMENT column in this case is blank.)

    In MySQL 5.1, there is also only one record in the PARTITIONS table for a table using the NDBCluster storage engine. The same columns are also NULL (or empty) as for a non-partitioned table.

22.20. The INFORMATION_SCHEMA EVENTS Table

The EVENTS table provides information about scheduled events, which are discussed in Chapter 20, Event Scheduler.

INFORMATION_SCHEMA NameSHOW NameRemarks
EVENT_CATALOG NULL, MySQL extension
EVENT_SCHEMADbMySQL extension
EVENT_NAMENameMySQL extension
DEFINERDefinerMySQL extension
EVENT_BODY MySQL extension
EVENT_DEFINITION MySQL extension
EVENT_TYPETypeMySQL extension
EXECUTE_ATExecute atMySQL extension
INTERVAL_VALUEInterval valueMySQL extension
INTERVAL_FIELDInterval fieldMySQL extension
SQL_MODE MySQL extension
STARTSStartsMySQL extension
ENDSEndsMySQL extension
STATUSStatusMySQL extension
ON_COMPLETION MySQL extension
CREATED MySQL extension
LAST_ALTERED MySQL extension
LAST_EXECUTED MySQL extension
EVENT_COMMENT MySQL extension

Notes:

  • The EVENTS table is a non-standard table. It was added in MySQL 5.1.6.

  • EVENT_CATALOG: The value of this column is always NULL.

  • EVENT_SCHEMA: The name of the schema (database) to which this event belongs.

  • EVENT_NAME: The name of the event.

  • DEFINER: The user who created the event. Always displayed in 'user_name'@'host_name' format.

  • EVENT_BODY: The language used for the statements in the event's DO clause; in MySQL 5.1, this is always SQL.

    This column was added in MySQL 5.1.12. It is not to be confused with the column of the same name (now named EVENT_DEFINITION) that existed in earlier MySQL versions.

  • EVENT_DEFINITION: The text of the SQL statement making up the event's DO clause; in other words, the statement executed by this event.

    Note: Prior to MySQL 5.1.12, this column was named EVENT_BODY.

  • EVENT_TYPE: One of the two values ONE TIME or RECURRING.

  • EXECUTE_AT: For a one-time event, this is the DATETIME value specified in the AT clause of the CREATE EVENT statement used to create the event, or of the last ALTER EVENT statement that modified the event. The value shown in this column reflects the addition or subtraction of any INTERVAL value included in the event's AT clause. For example, if an event is created using ON SCHEDULE AT CURRENT_TIMESTAMP + '1:6' DAY_HOUR, and the event was created at 2006-02-09 14:05:30, the value shown in this column would be '2006-02-10 20:05:30'.

    If the event's timing is determined by an EVERY clause instead of an AT clause (that is, if the event is recurring), the value of this column is NULL.

  • INTERVAL_VALUE: For recurring events, this column contains the numeric portion of the event's EVERY clause.

    For a one-time event (that is, an event whose timing is determined by an AT clause), this column's value is NULL.

  • INTERVAL_FIELD: For recurring events, this column contains the units portion of the EVERY clause governing the timing of the event, prefixed with 'INTERVAL_'. Thus, this column contains a value such as 'INTERVAL_YEAR', 'INTERVAL_QUARTER', 'INTERVAL_DAY', and so on.

    For a one-time event (that is, an event whose timing is determined by an AT clause), this column's value is NULL.

  • SQL_MODE: The SQL mode in effect at the time the event was created or altered.

  • STARTS: For a recurring event whose definition includes a STARTS clause, this column contains the corresponding DATETIME value. As with the EXECUTE_AT column, this value resolves any expressions used.

    If there is no STARTS clause affecting the timing of the event, this column is empty. (Prior to MySQL 5.1.8, it contained NULL in such cases.)

  • ENDS: For a recurring event whose definition includes a ENDS clause, this column contains the corresponding DATETIME value. As with the EXECUTE_AT column (see previous example), this value resolves any expressions used.

    If there is no ENDS clause affecting the timing of the event, this column contains NULL.

  • STATUS: One of the two values ENABLED or DISABLED.

  • ON_COMPLETION: One of the two values PRESERVE or NOT PRESERVE.

  • CREATED: The date and time when the event was created. This is a DATETIME value.

  • LAST_ALTERED: The date and time when the event was last modified. This is a DATETIME value. If the event has not been modified since its creation, this column holds the same value as the CREATED column.

  • LAST_EXECUTED: The date and time when the event last executed. A DATETIME value. If the event has never executed, this column's value is NULL.

  • EVENT_COMMENT: The text of a comment, if the event has one. If there is no comment, the value of this column is an empty string.

Example: Suppose the user jon@ghidora creates an event named e_daily, and then modifies it a few minutes later using an ALTER EVENT statement, as shown here:

DELIMITER |

CREATE EVENT e_daily
    ON SCHEDULE EVERY 1 DAY
    STARTS CURRENT_TIMESTAMP + INTERVAL 6 HOUR
    DISABLE
    COMMENT 'Saves total number of sessions and
             clears the table once per day.'
    DO
      BEGIN
        INSERT INTO site_activity.totals (when, total)
          SELECT CURRENT_TIMESTAMP, COUNT(*) 
          FROM site_activity.sessions;
        DELETE FROM site_activity.sessions;
      END |

DELIMITER ;

ALTER EVENT e_daily
    ENABLED;

(Note that comments can span multiple lines.)

This user can then run the following SELECT statement, and obtain the output shown:

mysql> SELECT * FROM INFORMATION_SCHEMA.EVENTS
     > WHERE EVENT_NAME = 'e_daily' 
     > AND EVENT_SCHEMA = 'myschema'\G

*************************** 1. row ***************************
  EVENT_CATALOG: NULL
   EVENT_SCHEMA: myschema
     EVENT_NAME: e_daily
        DEFINER: jon@ghidora
     EVENT_BODY: BEGIN
                   INSERT INTO site_activity.totals (when, total)
                     SELECT CURRENT_TIMESTAMP, COUNT(*) 
                       FROM site_activity.sessions;
                   DELETE FROM site_activity.sessions;
                 END
     EVENT_TYPE: RECURRING
     EXECUTE_AT: NULL
 INTERVAL_VALUE: 1
 INTERVAL_FIELD: INTERVAL_DAY
       SQL_MODE: NULL
         STARTS: 2006-02-09 10:41:23
           ENDS: NULL
         STATUS: ENABLED
  ON_COMPLETION: DROP
        CREATED: 2006-02-09 14:35:35
   LAST_ALTERED: 2006-02-09 14:41:23
  LAST_EXECUTED: NULL
  EVENT_COMMENT: Saves total number of sessions and
                 clears the table once per day.
1 row in set (0.50 sec)

Important: The times displayed by the STARTS, ENDS, and LAST_EXECUTED columns are currently given in terms of Universal Time (GMT or UTC), regardless of the the server's time zone setting. (The same is true for the starts, ends, and last_executed columns of the mysql.event table and the Starts and Ends columns in the output of SHOW [FULL] EVENTS.) The CREATED and LAST_ALTERED columns use the server time zone (as do the created and last_altered columns of the mysql.event table).

For example, the e_daily event shown previously was created on a computer in Brisbane, Australia, at 14:35:35 on the 9th of February, 2006, Eastern Australia Standard Time, which can also be expressed as the GMT+10.00 time zone. The event definition was updated (using ALTER EVENT as shown earlier in this section) a few minutes later, at 14:41:23. These are the values displayed for CREATED and LAST_ALTERED. The event is scheduled to begin executing 6 hours later — that is, at 20:41:23 on the same date, local time. Subtracting 10 hours from this to obtain Universal Time yields 10:41:23, and it is this value that is shown for STARTS.

This use of Universal Time should not be relied upon in applications, as it is expected to change to server local time in an upcoming MySQL release. (Bug#16420)

See also Section 13.5.4.15, “SHOW EVENTS.

22.21. The INFORMATION_SCHEMA FILES Table

The FILES table provides information about the files in which MySQL NDB Disk Data tables are stored.

INFORMATION_SCHEMA NameSHOW NameRemarks
FILE_ID MySQL extension
FILE_NAME MySQL extension
FILE_TYPE MySQL extension
TABLESPACE_NAME MySQL extension
TABLE_CATALOG MySQL extension
TABLE_SCHEMA MySQL extension
TABLE_NAME MySQL extension
LOGFILE_GROUP_NAME MySQL extension
LOGFILE_GROUP_NUMBER MySQL extension
ENGINE MySQL extension
FULLTEXT_KEYS MySQL extension
DELETED_ROWS MySQL extension
UPDATE_COUNT MySQL extension
FREE_EXTENTS MySQL extension
TOTAL_EXTENTS MySQL extension
EXTENT_SIZE MySQL extension
INITIAL_SIZE MySQL extension
MAXIMUM_SIZE MySQL extension
AUTOEXTEND_SIZE MySQL extension
CREATION_TIME MySQL extension
LAST_UPDATE_TIME MySQL extension
LAST_ACCESS_TIME MySQL extension
RECOVER_TIME MySQL extension
TRANSACTION_COUNTER MySQL extension
VERSION MySQL extension
ROW_FORMAT MySQL extension
TABLE_ROWS MySQL extension
AVG_ROW_LENGTH MySQL extension
DATA_LENGTH MySQL extension
MAX_DATA_LENGTH MySQL extension
INDEX_LENGTH MySQL extension
DATA_FREE MySQL extension
CREATE_TIME MySQL extension
UPDATE_TIME MySQL extension
CHECK_TIME MySQL extension
CHECKSUM MySQL extension
STATUS MySQL extension
EXTRA MySQL extension

Notes:

  • FILE_ID column values are auto-generated.

  • FILE_NAME is the name of an UNDO log file created by CREATE LOGFILE GROUP or ALTER LOGFILE GROUP, or of a data file created by CREATE TABLESPACE or ALTER TABLESPACE.

  • FILE_TYPE is one of the values UNDOFILE or DATAFILE.

  • TABLESPACE_NAME is the name of the tablespace with which the file is associated.

  • In MySQL 5.1, the value of the TABLESPACE_CATALOG column is always NULL.

  • TABLE_NAME is the name of the Disk Data table with which the file is associated, if any.

  • The LOGFILE_GROUP_NAME column gives the name of the log file group to which the log file or data file belongs.

  • For an UNDO log file, the LOGFILE_GROUP_NUMBER contains the auto-generated ID number of the log file group to which the log file belongs.

  • For a MySQL Cluster Disk Data log file or data file, the value of the ENGINE column is always NDB or NDBCLUSTER.

  • For a MySQL Cluster Disk Data log file or data file, the value of the FULLTEXT_KEYS column is always empty.

  • The FREE EXTENTS column displays the number of extents which have not yet been used by the file. The TOTAL EXTENTS column show the total number of extents allocated to the file.

    The difference between these two columns is the number of extents currently in use by the file:

    SELECT TOTAL_EXTENTS - FREE_EXTENTS AS extents_used
        FROM INFORMATION_SCHEMA.FILES
        WHERE FILE_NAME = 'myfile.dat';
    

    You can approximate the amount of disk space in use by the file by multiplying this difference by the value of the EXTENT_SIZE column, which gives the size of an extent for the file in bytes:

    SELECT (TOTAL_EXTENTS - FREE_EXTENTS) * EXTENT_SIZE AS bytes_used
        FROM INFORMATION_SCHEMA.FILES
        WHERE FILE_NAME = 'myfile.dat';    
    

    Similarly, you can estimate the amount of space that remains available in a given file by multiplying FREE_EXTENTS by EXTENT_SIZE:

    SELECT FREE_EXTENTS * EXTENT_SIZE AS bytes_free
        FROM INFORMATION_SCHEMA.FILES
        WHERE FILE_NAME = 'myfile.dat';    
    

    Important: The byte values produced by the preceding queries are approximations only, and their precision is inversely proportional to the value of EXTENT_SIZE. That is, the larger EXTENT_SIZE becomes, the less accurate the approximations are.

    It is also important to remember that once an extent is used, it cannot be freed again without dropping the data file of which it is a part. This means that deletes from a Disk Data table do not release disk space.

    The extent size can be set in a CREATE TABLESPACE statement. See Section 13.1.9, “CREATE TABLESPACE Syntax”, for more information.

  • The INITIAL_SIZE column shows the size in bytes of the file. This is the same value that was used in the INITIAL_SIZE clause of the CREATE LOGFILE GROUP, ALTER LOGFILE GROUP, CREATE TABLESPACE, or ALTER TABLESPACE statement used to create the file.

    For MySQL 5.1 Cluster Disk Data files, the value of the MAXIMUM_SIZE column is always the same as INITIAL_SIZE, and the AUTOEXTEND_SIZE column is always empty.

  • The CREATION_TIME column shows the date and time when the file was created. The LAST_UPDATE_TIME column displays the date and time when the file was last modified. The LAST_ACCESSED column provides the date and time when the file was last accessed by the server.

    Currently, the values of these columns are as reported by the operating system, and are not supplied by the NDB storage engine. Where no value is provided by the operating system, these columns display 0000-00-00 00:00:00.

  • For MySQL Cluster Disk Data files, the value of the RECOVER_TIME and TRANSACTION_COUNTER columns is always 0.

  • For MySQL 5.1 Cluster Disk Data files, the following columns are always NULL:

    • VERSION

    • ROW_FORMAT

    • TABLE_ROWS

    • AVG_ROW_LENGTH

    • DATA_LENGTH

    • MAX_DATA_LENGTH

    • INDEX_LENGTH

    • DATA_FREE

    • CREATE_TIME

    • UPDATE_TIME

    • CHECK_TIME

    • CHECKSUM

  • For MySQL Cluster Disk Data files, the value of the STATUS column is always NORMAL.

  • For MySQL Cluster Disk Data files, the EXTRA column shows which data node the file belongs to, as each data node has its own copy of the file. For example, suppose you use this statement on a MySQL Cluster with four data nodes:

    CREATE LOGFILE GROUP mygroup
        ADD UNDOFILE 'new_undo.dat'
        INITIAL_SIZE 2G
        ENGINE NDB;
    

    After running the CREATE LOGFILE GROUP statement successfully, you should see a result similar to the one shown here for this query against the FILES table:

    mysql> SELECT LOGFILE_GROUP_NAME, FILE_TYPE, EXTRA
        ->     FROM INFORMATION_SCHEMA.FILES
        ->     WHERE FILE_NAME = 'new_undo.dat';
    +--------------------+-------------+----------------+
    | LOGFILE_GROUP_NAME | FILE_TYPE   | EXTRA          |
    +--------------------+-------------+----------------+
    | mygroup            | UNDO FILE   | CLUSTER_NODE=3 |
    | mygroup            | UNDO FILE   | CLUSTER_NODE=4 |
    | mygroup            | UNDO FILE   | CLUSTER_NODE=5 |
    | mygroup            | UNDO FILE   | CLUSTER_NODE=6 |
    +--------------------+-------------+----------------+
    4 rows in set (0.01 sec)
    
  • The FILES table is a non-standard table. It was added in MySQL 5.1.6.

  • There are no SHOW commands associated with the FILES table.

  • For additional examples using the FILES table to obtain information about Cluster Disk Data tables, see Section 15.11, “MySQL Cluster Disk Data Storage”.

22.22. The INFORMATION_SCHEMA PROCESSLIST Table

The PROCESSLIST table provides information about which threads are running.

INFORMATION_SCHEMA NameSHOW NameRemarks
IDIdMySQL extension
USERUserMySQL extension
HOSTHostMySQL extension
DBdbMySQL extension
COMMANDCommandMySQL extension
TIMETimeMySQL extension
STATEStateMySQL extension
INFOInfoMySQL extension

For an extensive description of the table columns, see Section 13.5.4.24, “SHOW PROCESSLIST Syntax”.

Notes:

  • The PROCESSLIST table is a non-standard table. It was added in MySQL 5.1.7.

  • Like the output from the corresponding SHOW statement, the PROCESSLIST table will only show information about your own threads, unless you have the PROCESS privilege, in which case you will see information about other threads, too. As an anonymous user, you cannot see any rows at all.

  • If an SQL statement refers to INFORMATION_SCHEMA.PROCESSLIST, then MySQL will populate the entire table once, when statement execution begins, so there is read consistency during the statement. There is no read consistency for a multi-statement transaction, though.

The following statements are equivalent:

SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST

SHOW PROCESSLIST

22.23. The INFORMATION_SCHEMA REFERENTIAL_CONSTRAINTS Table

The REFERENTIAL_CONSTRAINTS table provides information about foreign keys.

INFORMATION_SCHEMA NameSHOW NameRemarks
CONSTRAINT_CATALOG NULL
CONSTRAINT_SCHEMA  
CONSTRAINT_NAME  
UNIQUE_CONSTRAINT_CATALOG NULL
UNIQUE_CONSTRAINT_SCHEMA  
UNIQUE_CONSTRAINT_NAME  
MATCH_OPTION  
UPDATE_RULE  
DELETE_RULE  
TABLE_NAME  

Notes:

  • The REFERENTIAL_CONSTRAINTS table was added in MySQL 5.1.10.

  • TABLE_NAME has the same value as TABLE_NAME in INFORMATION_SCHEMA.TABLE_CONSTRAINTS.

  • CONSTRAINT_SCHEMA and CONSTRAINT_NAME identify the foreign key.

  • UNIQUE_CONSTRAINT_SCHEMA and UNIQUE_CONSTRAINT_NAME identify the referenced key.

  • The only valid value at this time for MATCH_OPTION is NONE.

  • The possible values for UPDATE_RULE or DELETE_RULE are CASCADE, SET NULL, SET DEFAULT, RESTRICT, NO ACTION.

22.24. The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables

The GLOBAL_STATUS and SESSION_STATUS tables provide information about server status variables. Their contents correspond to the information produced by the SHOW GLOBAL STATUS and SHOW SESSION STATUS statements (see Section 13.5.4.26, “SHOW STATUS Syntax”).

INFORMATION_SCHEMA NameSHOW NameRemarks
VARIABLE_NAMEVariable_name 
VARIABLE_VALUEValue 

Notes:

  • The GLOBAL_STATUS and SESSION_STATUS tables were added in MySQL 5.1.12.

  • The VARIABLE_VALUE column has the BIGINT type. The few status variables that have non-integer values are coerced to BIGINT values.

22.25. The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables

The GLOBAL_VARIABLES and SESSION_VARIABLES tables provide information about server status variables. Their contents correspond to the information produced by the SHOW GLOBAL VARIABLES and SHOW SESSION VARIABLES statements (see Section 13.5.4.30, “SHOW VARIABLES Syntax”).

INFORMATION_SCHEMA NameSHOW NameRemarks
VARIABLE_NAMEVariable_name 
VARIABLE_VALUEValue 

Notes:

  • The GLOBAL_VARIABLES and SESSION_VARIABLES tables were added in MySQL 5.1.12.

22.26. Other INFORMATION_SCHEMA Tables

We intend to implement additional INFORMATION_SCHEMA tables. In particular, we acknowledge the need for the PARAMETERS table.

22.27. Extensions to SHOW Statements

Some extensions to SHOW statements accompany the implementation of INFORMATION_SCHEMA:

  • SHOW can be used to get information about the structure of INFORMATION_SCHEMA itself.

  • Several SHOW statements accept a WHERE clause that provides more flexibility in specifying which rows to display.

INFORMATION_SCHEMA is an information database, so its name is included in the output from SHOW DATABASES. Similarly, SHOW TABLES can be used with INFORMATION_SCHEMA to obtain a list of its tables:

mysql> SHOW TABLES FROM INFORMATION_SCHEMA;
+---------------------------------------+
| Tables_in_information_schema          |
+---------------------------------------+
| CHARACTER_SETS                        |
| COLLATIONS                            |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS                               |
| COLUMN_PRIVILEGES                     |
| ENGINES                               |
| EVENTS                                |
| FILES                                 |
| KEY_COLUMN_USAGE                      |
| PARTITIONS                            |
| PLUGINS                               |
| PROCESSLIST                           |
| ROUTINES                              |
| SCHEMATA                              |
| SCHEMA_PRIVILEGES                     |
| STATISTICS                            |
| TABLES                                |
| TABLE_CONSTRAINTS                     |
| TABLE_PRIVILEGES                      |
| TRIGGERS                              |
| USER_PRIVILEGES                       |
| VIEWS                                 |
+---------------------------------------+
22 rows in set (0.04 sec)

SHOW COLUMNS and DESCRIBE can display information about the columns in individual INFORMATION_SCHEMA tables.

Several SHOW statement have been extended to allow a WHERE clause:

SHOW CHARACTER SET
SHOW COLLATION
SHOW COLUMNS
SHOW DATABASES
SHOW FUNCTION STATUS
SHOW KEYS
SHOW OPEN TABLES
SHOW PROCEDURE STATUS
SHOW STATUS
SHOW TABLE STATUS
SHOW TABLES
SHOW VARIABLES

The WHERE clause, if present, is evaluated against the column names displayed by the SHOW statement. For example, the SHOW CHARACTER SET statement produces these output columns:

mysql> SHOW CHARACTER SET;
+----------+-----------------------------+---------------------+--------+
| Charset  | Description                 | Default collation   | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese    | big5_chinese_ci     |      2 |
| dec8     | DEC West European           | dec8_swedish_ci     |      1 |
| cp850    | DOS West European           | cp850_general_ci    |      1 |
| hp8      | HP West European            | hp8_english_ci      |      1 |
| koi8r    | KOI8-R Relcom Russian       | koi8r_general_ci    |      1 |
| latin1   | cp1252 West European        | latin1_swedish_ci   |      1 |
| latin2   | ISO 8859-2 Central European | latin2_general_ci   |      1 |
...

To use a WHERE clause with SHOW CHARACTER SET, you would refer to those column names. As an example, the following statement displays information about character sets for which the default collation contains the string 'japanese':

mysql> SHOW CHARACTER SET WHERE `Default collation` LIKE '%japanese%';
+---------+---------------------------+---------------------+--------+
| Charset | Description               | Default collation   | Maxlen |
+---------+---------------------------+---------------------+--------+
| ujis    | EUC-JP Japanese           | ujis_japanese_ci    |      3 |
| sjis    | Shift-JIS Japanese        | sjis_japanese_ci    |      2 |
| cp932   | SJIS for Windows Japanese | cp932_japanese_ci   |      2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci |      3 |
+---------+---------------------------+---------------------+--------+

This statement displays the multi-byte character sets:

mysql> SHOW CHARACTER SET WHERE Maxlen > 1;
+---------+---------------------------+---------------------+--------+
| Charset | Description               | Default collation   | Maxlen |
+---------+---------------------------+---------------------+--------+
| big5    | Big5 Traditional Chinese  | big5_chinese_ci     |      2 |
| ujis    | EUC-JP Japanese           | ujis_japanese_ci    |      3 |
| sjis    | Shift-JIS Japanese        | sjis_japanese_ci    |      2 |
| euckr   | EUC-KR Korean             | euckr_korean_ci     |      2 |
| gb2312  | GB2312 Simplified Chinese | gb2312_chinese_ci   |      2 |
| gbk     | GBK Simplified Chinese    | gbk_chinese_ci      |      2 |
| utf8    | UTF-8 Unicode             | utf8_general_ci     |      3 |
| ucs2    | UCS-2 Unicode             | ucs2_general_ci     |      2 |
| cp932   | SJIS for Windows Japanese | cp932_japanese_ci   |      2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci |      3 |
+---------+---------------------------+---------------------+--------+