在一个多列索引(x,y,z)上查询列(x,z)。
现有的主键索引应该足够满足这种情况,因为使用PRIMARY KEY (x, y, z)
实际上就相当于有了一个覆盖索引
。查看什么是覆盖索引?
However, if there is a specific need to query on columns (x, z) for a multi-column index (x, y, z), it is possible to create such an index to optimize the query performance.
然而,如果有特定的需要在多列索引(x, y, z)上查询列(x, z),可以创建这样的索引来优化查询性能。
To create a multi-column index, the following SQL statement can be used:
为了创建一个多列索引,可以使用以下SQL语句:
CREATE INDEX index_name ON table_name (x, y, z);
This statement creates an index called "index_name" on the table "table_name" with the columns (x, y, z) in that order.
这个语句在表"table_name"上创建一个索引"index_name",索引的列按照(x, y, z)的顺序排列。
Once the index is created, queries that involve the columns (x, z) will benefit from the index and the query performance will be improved.
索引创建完成后,涉及到列(x, z)的查询将受益于索引,查询性能将得到提高。
In summary, if there is a need to query on specific columns for a multi-column index, it is recommended to create a separate index on those columns to optimize the query performance.