Mysql show index解释
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内容图文
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. |
原文：http://blog.51cto.com/wangergui/2074486
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