Mysql show index解释
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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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