考虑我有3个问题类型；真或假ToF、多选MC和完全。
现在我想随机得到10个问题是真是假，5个问题是多选，2个问题是完整的（这些数字不是静态的，它将是执行函数的变量）。
我的桌子是这样的：
+-----+----------------------------------------------------+----------+--------+
| id | question | type | examId |
+-----+----------------------------------------------------+----------+--------+
| 1 | true or false question 1 | ToF | 1 |
| 2 | true or false question 2 | ToF | 1 |
| 3 | true or false question 3 | ToF | 1 |
| 4 | true or false question 4 | ToF | 1 |
| 5 | true or false question 5 | ToF | 1 |
| 6 | true or false question 6 | ToF | 1 |
| 7 | true or false question 7 | ToF | 1 |
| 8 | true or false question 8 | ToF | 1 |
| 9 | true or false question 9 | ToF | 1 |
| 10 | true or false question 10 | ToF | 1 |
| 11 | true or false question 11 | ToF | 1 |
| 12 | true or false question 12 | ToF | 1 |
| 13 | multi choice question 1 | MC | 1 |
| 14 | multi choice question 2 | MC | 1 |
| 15 | multi choice question 3 | MC | 1 |
| 16 | multi choice question 4 | MC | 1 |
| 17 | multi choice question 5 | MC | 1 |
| 18 | multi choice question 6 | MC | 1 |
| 19 | multi choice question 7 | MC | 1 |
| 20 | multi choice question 8 | MC | 1 |
| 21 | complete question 1 | complete | 1 |
| 22 | complete question 2 | complete | 1 |
| 23 | complete question 3 | complete | 1 |
| 24 | complete question 4 | complete | 1 |
| 25 | complete question 5 | complete | 1 |
| 26 | complete question 6 | complete | 1 |
| 27 | complete question 7 | complete | 1 |
+-----+----------------------------------------------------+----------+--------+
到目前为止，我尝试的是为每种类型写一个类似的查询
SELECT * FROM question WHERE type = 'ToF' ORDER BY rand() LIMIT 10
SELECT * FROM question WHERE type = 'MC' ORDER BY rand() LIMIT 5
SELECT * FROM question WHERE type = 'complete' ORDER BY rand() LIMIT 2
我可以只使用一个查询吗？
把所有结果按类型排序，然后用PHP得到我想要的随机结果，这好吗？
您可以在一个查询中完成这一切。甚至最后的随机化：
(SELECT * FROM question WHERE type = 'ToF' ORDER BY rand() LIMIT 10
) UNION ALL
(SELECT * FROM question WHERE type = 'MC' ORDER BY rand() LIMIT 5
) UNION ALL
(SELECT * FROM question WHERE type = 'complete' ORDER BY rand() LIMIT 2
)
ORDER BY rand();
这是一个合理的方法——如果你只有少数已知的类型。