Mysql show index解释

发布时间：2020-07-16 19:30:29 作者：Abigale2018
来源：网络阅读：1956

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.

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