MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
The STATISTICS table provides
information about table indexes.
The STATISTICS table has these
columns:
TABLE_CATALOG
The name of the catalog to which the table containing the
index belongs. This value is always def.
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 always PRIMARY.
SEQ_IN_INDEX
The column sequence number in the index, starting with 1.
COLUMN_NAME
The column name. See also the description for the
EXPRESSION column.
COLLATION
How the column is sorted in the index. This can have values
A (ascending), D
(descending), or NULL (not sorted).
CARDINALITY
An estimate of the number of unique values in the index. To
update this number, run ANALYZE
TABLE or (for MyISAM 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.
Prefix limits are measured in bytes.
However, prefix lengths for index
specifications in CREATE
TABLE, ALTER TABLE,
and CREATE 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, see Section 8.3.4, “Column Indexes”, and Section 13.1.14, “CREATE INDEX Statement”.
PACKED
Indicates how the key is packed. NULL if it
is not.
NULLABLE
Contains YES if the column may contain
NULL 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 as disabled if the index is disabled.
INDEX_COMMENT
Any comment provided for the index with a
COMMENT attribute when the index was
created.
There is no standard INFORMATION_SCHEMA
table for indexes. The MySQL column list is similar to what
SQL Server 2000 returns for sp_statistics,
except that QUALIFIER and
OWNER are replaced with
CATALOG and SCHEMA,
respectively.
Information about table indexes is also available from the
SHOW INDEX statement. See
Section 13.7.5.22, “SHOW INDEX Statement”. The following statements are
equivalent:
SELECT * FROM INFORMATION_SCHEMA.STATISTICS WHERE table_name = 'tbl_name' AND table_schema = 'db_name' SHOW INDEX FROMtbl_nameFROMdb_name