mysql STRAIGHT_JOIN
时间: 2023-08-26 21:17:31 浏览: 115
MySQL中的STRAIGHT_JOIN是一种查询优化提示,用于指示MySQL优化器以指定的连接顺序执行表之间的连接操作,而不是根据优化器的默认选择。
当使用STRAIGHT_JOIN时,MySQL将按照查询中指定的连接顺序执行连接操作,而不会重新排序表的顺序。这可以用于强制查询使用特定的连接顺序,以获得更好的性能。
下面是一个使用STRAIGHT_JOIN的示例:
相关问题
MySQL straight_join
MySQL `STRAIGHT_JOIN` is a query modifier that instructs the MySQL optimizer to join the tables in the order they are specified in the `FROM` clause. Normally, the optimizer decides the join order based on the cost-based optimization algorithm, which may not always result in the best performance. By using `STRAIGHT_JOIN`, you can force MySQL to use the join order you specified, which may be more efficient in certain cases.
Here's an example of using `STRAIGHT_JOIN`:
```
SELECT *
FROM table1 STRAIGHT_JOIN table2 ON table1.id = table2.id
WHERE table1.column = 'value';
```
In this example, we are joining `table1` and `table2` on the `id` column, and filtering the result by the `column` value in `table1`. By using `STRAIGHT_JOIN`, we are telling MySQL to join `table1` and `table2` in the order they are specified in the `FROM` clause.
straight_join
straight_join是MySQL中的一种查询优化指令。它只适用于inner join,而不适用于left join和right join。使用straight_join可以让左表驱动右表,改变表的执行顺序,以提高查询性能。然而,使用straight_join需要谨慎,因为有些情况下优化器的判断可能更加准确。尽可能让优化器自行决定执行顺序,除非有明确的理由需要手动指定执行顺序。一个使用straight_join的示例查询可以是:select * from t2 straight_join t1 on t2.a = t1.a; <span class="em">1</span><span class="em">2</span><span class="em">3</span>
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