Mysql Show Index explanation

查看表上的索引状态:




SHOW INDEXReturns table index information.

SHOW KEYSand is SHOW INDEXES synonyms for SHOW INDEX .

Grammar:

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

The following fields is returned by SHOW INDEX .

Field	Description
Table	Table Name
Non_unique	1If 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 is calculated at various times, and can help the optimizer make improved decisions.
Sub_part	NULLIf the entire column is included in the index, or the number of included characters if not.
Packed	NULLIf the index is not packed, otherwise how the index is packed.
Null	NULLIf NULL values is permitted in the column, an empty string if NULL ' s is 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.

Mysql Show Index explanation