为每列获取不同的值，而无需重新执行相同的查询

Question

有没有办法根据MySQL中的查询返回唯一值，而无需为每列重新执行相同的查询？

我有一个有点复杂的查询，其中包含一些连接，可能会返回50,000多行。我的目标是获得每列的所有唯一值，就像我已经完成的那样：

SELECT DISTINCT column_a FROM ...

每列。如果不多次运行查询，有没有办法完成这项工作？

Answer 1

您可以使用列子查询。例子

  mysql> select (select name from city order by rand() limit 1) "randdom value1", (select name from city order by rand() limit 1) "random value2", name "actual value" from city limit 10;

+--------------------+-------------------+----------------+
| randdom value1     | random value2     | actual value   |
+--------------------+-------------------+----------------+
| Valle de Santiago  | Shulin            | Kabul          |
| Ibarra             | Xiangfan          | Qandahar       |
| Kingston upon Hull | Bataisk           | Herat          |
| Huancayo           | Fort Worth        | Mazar-e-Sharif |
| Longyan            | Linköping         | Amsterdam      |
| Cheju              | Rubtsovsk         | Rotterdam      |
| Aligarh            | Bergisch Gladbach | Haag           |
| Najran             | Pultava [Poltava] | Utrecht        |
| Shuangyashan       | Cedar Rapids      | Eindhoven      |
| Buffalo            | Abilene           | Tilburg        |
+--------------------+-------------------+----------------+
10 rows in set (0.03 sec)