查看表上的索引状态:


SHOW INDEX returns table index information.


SHOW KEYS and SHOW INDEXES are synonyms for SHOW INDEX.


语法:


show {index|indexes} from table_name [ from db_name ] [where expr]


The following fields are returned by SHOW INDEX.


Field Description
Table Table name
Non_unique 1 if the index permits duplicate values, 0 if values must be unique.
Key_name Index name. The primary key is always named PRIMARY.
Seq_in_index The column's sequence in the index, beginning with 1.
Column_name Column name.
Collation Either A, if the column is sorted in ascending order in the index, or NULL if it's not sorted.
Cardinality Estimated number of unique values in the index. The cardinality statistics are calculated at various times, and can help the optimizer make improved decisions.
Sub_part NULL if the entire column is included in the index, or the number of included characters if not.
Packed NULL if the index is not packed, otherwise how the index is packed.
Null NULL if NULL values are permitted in the column, an empty string if NULL's are not permitted.
Index_type The index type, which can be BTREE, FULLTEXT, HASH or RTREE. See Storage Engine Index Types.
Comment Other information, such as whether the index is disabled.
Index_comment Contents of the COMMENT attribute when the index was created.