mysql - 在 mysql 上组合 4 个 SELECT 查询

Question

我正在尝试组合这 3 个 mysql 语句。我一直在使用 UNION 和 JOIN 关键字，但它没有提供我想要的输出。有什么建议么？这是我的 3 个声明。

SELECT * FROM entrancequestion
WHERE Subject='Abstract Reasoning'
ORDER BY RAND()
LIMIT 10

SELECT * FROM entrancequestion
WHERE Subject='English'
ORDER BY RAND()
LIMIT 30

SELECT * FROM entrancequestion
WHERE Subject='Mathematics'
ORDER BY RAND()
LIMIT 30

SELECT * FROM entrancequestion
WHERE Subject='Science'
ORDER BY RAND()
LIMIT 30

我尝试像这样组合前 2 个语句:

SELECT * FROM entrancequestion
WHERE Subject='Abstract Reasoning'
LIMIT 10
UNION
SELECT * FROM entrancequestion
WHERE Subject='English'
ORDER BY RAND()
LIMIT 30;

但是它只读取第二个 LIMIT 查询，其中 t 只输出 30 行。

我想创建一个查询，其中总共显示 100 行并根据索引随机显示。非常感谢您的帮助。

Answer 1

引用docs ,

要将 ORDER BY 或 LIMIT 应用于单个 SELECT，请将子句放在包含 SELECT 的括号内:

(SELECT * FROM entrancequestion
WHERE Subject='Abstract Reasoning'
ORDER BY RAND()
LIMIT 10)

UNION

(SELECT * FROM entrancequestion
WHERE Subject='English'
ORDER BY RAND()
LIMIT 30)

UNION

(SELECT * FROM entrancequestion
WHERE Subject='Mathematics'
ORDER BY RAND()
LIMIT 30)

UNION

(SELECT * FROM entrancequestion
WHERE Subject='Science'
ORDER BY RAND()
LIMIT 30 )