在另一个表上使用`where`子句从特定表中选择一个值 [英] Select a value from specific table with `where` clause on another table

问题描述

如何在单个MySQL查询中执行此类操作？

How can I do something like this in a Single MySQL Query?

select `value_a` 
from `table_1` 
where `value_b` = (select `value_b` from `table_2` where `value_c` = `x`);

我使用CodeIgniter，所以我可以使用活动记录。

I use CodeIgniter so I can use Active Records.

推荐答案

您也可以使用 JOIN ：

select t1.value_a
from table_1 t1
inner join table_2 t2
  on t1.value_b = t2.value_b
where t2.value_c = 'x'

您也可以使用现有的查询，但 / code>由反引号包围而不是单引号：

You can also use your existing query, but the x is surrounded by backticks and not single quotes:

select `value_a` 
from `table_1` 
where `value_b` = (select `value_b` from `table_2` where `value_c` = 'x);

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