具有多个不相关表的 SQL 查询

Question

在我的 mySQL 数据库中有四个表：breakfast、dinner、supper、supper。 这些表的列名相同。其中每个人都有一个名为“accepted”的列，等于0 或1。

我想做一个 SQL 查询，从这四个表中给我一个随机行 WHERE 'accepted' 列等于 0。

只有 1 个有效的表的 SQL 查询：

SELECT * FROM breakfast WHERE accepted=0 ORDER BY RAND() LIMIT 1

我的 SQL 查询版本有四个不起作用的表：

 SELECT * FROM breakfast, dinner, supper, dessert WHEREbreakfast.accepted=0
AND dinner.accepted=0 AND supper.accepted=0 AND dessert.accepted=0 ORDER BY RAND() LIMIT 1

Answer 1

这样试试，

我假设您在所有四个表中的列数都相同。

MySQL

   SELECT col1,col2
FROM (
    SELECT col1,col2
    FROM breakfast
    WHERE breakfast.accepted = 0

    UNION

    SELECT col1,col2
    FROM dinner
    WHERE dinner.accepted = 0

    UNION

    SELECT col1,col2
    FROM supper
    WHERE supper.accepted = 0

    UNION

    SELECT col1,col2
    FROM dessert
    WHERE dessert.accepted = 0
    ) T
ORDER BY RAND() LIMIT 1

SQL 服务器：

SELECT top 1 col1,col2
FROM (
    SELECT col1,col2
    FROM breakfast
    WHERE breakfast.accepted = 0

    UNION

    SELECT col1,col2
    FROM dinner
    WHERE dinner.accepted = 0

    UNION

    SELECT col1,col2
    FROM supper
    WHERE supper.accepted = 0

    UNION

    SELECT col1,col2
    FROM dessert
    WHERE dessert.accepted = 0
    ) T
ORDER BY newid()

Answer 2

试试这个：

SELECT breakfast FROM 
(SELECT breakfast FROM breakfast WHERE accepted=0 
union
SELECT supper as breakfast FROM supper WHERE accepted=0 
union
SELECT dessert as breakfast FROM dessert WHERE accepted=0 
union
SELECT dinner as breakfast FROM dinner WHERE accepted=0 
) food ORDER BY RAND() LIMIT 1 

在这个查询中，除了早餐表中有一个名称为早餐的字段，如果您需要使用“*”，请使用别名使所有字段名称在不同的联合查询中相似。

Answer 3

检查一下

 SELECT TOP 1 * FROM breakfast,
 (SELECT TOP 1 * FROM dinner WHERE accepted=0 ORDER BY RAND()) As Dinner,
 (SELECT TOP 1 * FROM supper WHERE accepted=0 ORDER BY RAND()) As supper,
 (SELECT TOP 1 * FROM dessert WHERE accepted=0 ORDER BY RAND()) As dessert 
 WHERE breakfast.accepted=0 ORDER BY RAND()