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Information Schema STATISTICS Table

The Information Schema STATISTICS table provides information about table indexes.

It contains the following columns:

Column	Description
`TABLE_CATALOG`	Always `def`.
`TABLE_SCHEMA`	Database name.
`TABLE_NAME`	Table name.
`NON_UNIQUE`	`1` if the index can have duplicates, `0` if not.
`INDEX_SCHEMA`	Database name.
`INDEX_NAME`	Index name. The primary key is always named `PRIMARY`.
`SEQ_IN_INDEX`	The column sequence number, starting at 1.
`COLUMN_NAME`	Column name.
`COLLATION`	`A` for sorted in ascending order, or `NULL` for unsorted.
`CARDINALITY`	Estimate of the number of unique values stored in the index based on statistics stored as integers. Higher cardinalities usually mean a greater chance of the index being used in a join. Updated by the ANALYZE TABLE statement or `myisamchk -a`.
`SUB_PART`	`NULL` if the whole column is indexed, or the number of indexed characters if partly indexed.
`PACKED`	`NULL` if not packed, otherwise how the index is packed.
`NULLABLE`	`YES` if the column may contain NULLs, empty string if not.
`INDEX_TYPE`	Index type, one of `BTREE`, `RTREE`, `HASH` or `FULLTEXT`. See Storage Engine Index Types.
`COMMENT`	Index comments from the `CREATE INDEX` statement.

The SHOW INDEX statement produces similar output.

Example

SELECT * FROM INFORMATION_SCHEMA.STATISTICS\G
...
*************************** 85. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: table1
   NON_UNIQUE: 1
 INDEX_SCHEMA: test
   INDEX_NAME: col2
 SEQ_IN_INDEX: 1
  COLUMN_NAME: col2
    COLLATION: A
  CARDINALITY: 6
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: 
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT:
...

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https://mariadb.com/kb/en/information-schema-statistics-table/