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. |
本文转自 wangergui 51CTO博客，原文链接：http://blog.51cto.com/wangergui/2074486，如需转载请自行联系原作者
