Question

SELECT *
FROM table_a 
LEFT JOIN table_b ON (table_b.id = table_a.id) 
WHERE table_b.created BETWEEN ? AND ? 
      AND table_b.manager IN(
        SELECT DISTINCT (b.id) 
        FROM table_b a 
          INNER JOIN table_b b ON a.manager = b.id 
            AND b.user_level > 0
            AND b.id != 1
      )

如何在上述查询中删除子查询并使用JOINS

由于

Answer 1

MySQL 5.5（和更低版本）的优化器为IN (SELECT ...)生成DEPENDENT SUBQUERY，这意味着找到了每个匹配的行，IN(SELECT ...)被评估为使选择变慢。< / p>

简单优化查询是使内联视图如下：

SELECT *
FROM table_a LEFT JOIN table_b ON (table_b.id = table_a.id) 
    INNER JOIN (
            SELECT DISTINCT b.id AS id
            FROM table_b a 
              INNER JOIN table_b b ON a.manager = b.id 
                AND b.user_level > 0
                AND b.id != 1
    ) x ON table_b.manager = x.id
WHERE table_b.created BETWEEN ? AND ? 
  AND x.id IS NOT NULL;

我认为avobe查询会产生与你自己相同的效果。

最后，DISTINCT不是函数。请使用SELECT DISTINCT b.id而不是SELECT DISTINCT (b.id)

如何使用JOINS而不是子查询

1 个答案: