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[Mysql数据库] Mysql show index解释

发表于 2018-3-9 08:00:02

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.


FieldDescription
TableTable name
Non_unique1 if the index permits duplicate values, 0 if values must be unique.
Key_nameIndex name. The primary key is always named PRIMARY.
Seq_in_indexThe column's sequence in the index, beginning with 1.
Column_nameColumn name.
CollationEither A, if the column is sorted in ascending order in the index, or NULL if it's not sorted.
CardinalityEstimated number of unique values in the index. The cardinality statistics are calculated at various times, and can help the optimizer make improved decisions.
Sub_partNULL if the entire column is included in the index, or the number of included characters if not.
PackedNULL if the index is not packed, otherwise how the index is packed.
NullNULL if NULL values are permitted in the column, an empty string if NULL's are not permitted.
Index_typeThe index type, which can be BTREE, FULLTEXT, HASH or RTREE. See Storage Engine Index Types.
CommentOther information, such as whether the index is disabled.
Index_commentContents of the COMMENT attribute when the index was created.






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