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If theinnodb_read_only system variable is enabled,ANALYZE TABLE may fail because it cannot update statistics tables in the data dictionary, which useInnoDB. ForANALYZE TABLE operations that update the key distribution, failure may occur even if the operation updates the table itself (for example, if it is aMyISAM table). To obtain the updated distribution statistics, setinformation_schema_stats_expiry=0.

• TABLE_CATALOG

  The name of the catalog to which the table containing the index belongs. This value is alwaysdef.

• TABLE_SCHEMA

  The name of the schema (database) to which the table containing the index belongs.

• TABLE_NAME

  The name of the table containing the index.

• NON_UNIQUE

  0 if the index cannot contain duplicates, 1 if it can.

• INDEX_SCHEMA

  The name of the schema (database) to which the index belongs.

• INDEX_NAME

  The name of the index. If the index is the primary key, the name is alwaysPRIMARY.

• SEQ_IN_INDEX

  The column sequence number in the index, starting with 1.

• COLUMN_NAME

  The column name. See also the description for theEXPRESSION column.

• COLLATION

  How the column is sorted in the index. This can have valuesA (ascending),D (descending), orNULL (not sorted).

• CARDINALITY

  An estimate of the number of unique values in the index. To update this number, runANALYZE TABLE or (forMyISAM tables)myisamchk -a.

  CARDINALITY is counted based on statistics stored as integers, so the value is not necessarily exact even for small tables. The higher the cardinality, the greater the chance that MySQL uses the index when doing joins.

• SUB_PART

  The index prefix. That is, the number of indexed characters if the column is only partly indexed,NULL if the entire column is indexed.

  Note

  Prefixlimits are measured in bytes. However, prefixlengths for index specifications inCREATE TABLE,ALTER TABLE, andCREATE INDEX statements are interpreted as number of characters for nonbinary string types (CHAR,VARCHAR,TEXT) and number of bytes for binary string types (BINARY,VARBINARY,BLOB). Take this into account when specifying a prefix length for a nonbinary string column that uses a multibyte character set.

  For additional information about index prefixes, seeSection 10.3.5, “Column Indexes”, andSection 15.1.15, “CREATE INDEX Statement”.

• PACKED

  Indicates how the key is packed.NULL if it is not.

• NULLABLE

  ContainsYES if the column may containNULL values and'' if not.

• INDEX_TYPE

  The index method used (BTREE,FULLTEXT,HASH,RTREE).

• COMMENT

  Information about the index not described in its own column, such asdisabled if the index is disabled.

• INDEX_COMMENT

  Any comment provided for the index with aCOMMENT attribute when the index was created.

• IS_VISIBLE

  Whether the index is visible to the optimizer. SeeSection 10.3.12, “Invisible Indexes”.

• EXPRESSION

  MySQL 8.0.13 and higher supports functional key parts (seeFunctional Key Parts), which affects both theCOLUMN_NAME andEXPRESSION columns:

  • For a nonfunctional key part,COLUMN_NAME indicates the column indexed by the key part andEXPRESSION isNULL.

  • For a functional key part,COLUMN_NAME column isNULL andEXPRESSION indicates the expression for the key part.

• There is no standardINFORMATION_SCHEMA table for indexes. The MySQL column list is similar to what SQL Server 2000 returns forsp_statistics, except thatQUALIFIER andOWNER are replaced withCATALOG andSCHEMA, respectively.