Question

所以我试图让这个陈述起作用：

SELECT 
    *
FROM
    sakai.SAKAI_REALM AS sr
WHERE
    sr.REALM_KEY = (SELECT DISTINCT
            srrf.REALM_KEY
        FROM
            sakai.SAKAI_REALM_RL_FN AS srrf
        WHERE
            srrf.ROLE_KEY = 51);

但是我收到MySql错误1242，Subquery返回超过1行。我知道它会返回多行（它应该返回7）但有没有办法让这个查询起作用？我不怀疑我使用了错误的语法。

我正在尝试查找子查询中具有现有值的所有SAKAI_REALMS。

Answer 1

尝试将=更改为in，这基本上代表了从子查询返回的集合中的值：

SELECT 
*
FROM
sakai.SAKAI_REALM AS sr
WHERE
sr.REALM_KEY in (SELECT DISTINCT
        srrf.REALM_KEY
    FROM
        sakai.SAKAI_REALM_RL_FN AS srrf
    WHERE
        srrf.ROLE_KEY = 51);

Answer 2

使用联接，您可以执行以下操作：

SELECT sr.*
FROM sakai.SAKAI_REALM AS sr
INNER JOIN 
(
  SELECT DISTINCT srrf.REALM_KEY
  FROM sakai.SAKAI_REALM_RL_FN AS srrf
  WHERE srrf.ROLE_KEY = 51
) m ON sr.REALM_KEY = m.REALM_KEY

或者，如果子查询可能返回多个记录，则使用：

SELECT *
FROM sakai.SAKAI_REALM AS sr
WHERE sr.REALM_KEY IN 
(
  SELECT srrf.REALM_KEY
  FROM sakai.SAKAI_REALM_RL_FN AS srrf
  WHERE srrf.ROLE_KEY = 51
);

或者，强制它仅使用LIMIT 1返回一条记录：

SELECT *
FROM sakai.SAKAI_REALM AS sr
WHERE sr.REALM_KEY = 
(
  SELECT srrf.REALM_KEY
  FROM sakai.SAKAI_REALM_RL_FN AS srrf
  WHERE srrf.ROLE_KEY = 51
  LIMIT 1
);

使用多个选择的MySql语句出现问题

2 个答案: