带有“where in"的嵌套 MySql Select 语句条款 [英] Nested MySql Select statement with "where in" clause

问题描述

我会尽量详细说明这一点.我有一个带有 where in 子句的嵌套 select 语句，但是应该将 select 的嵌套部分解释为文字字符串(我相信这是正确的术语).然而 mysql 的默认行为导致了我不想要的结果.

I'll try to detail this the best I can. I have a nested select statement with a where in clause, but the nested part of the select should be interpreted as a literal string (I believe this is the right terminology). However the default behavior of mysql leads to a result I do not want.

即

select class 
from cs_item 
where code="007"

+-------+
| class |
+-------+
| 1,3   |
+-------+

如果我在选择查询中明确键入in (1,3)"，则以下是一个查询:

And the below is a query if I explicitly type "in (1,3)" as part of a select query:

select alpha,description 
from cs_quality 
where class in (1,3);

+-------+-------------+
| alpha | description |
+-------+-------------+
| STD   | STD         |
| XS    | XS          |
| 5     | Sch 5       |
| 10    | Sch 10      |
| 20    | Sch 20      |
| 40    | Sch 40      |
| 60    | Sch 60      |
| 80    | Sch 80      |
| 100   | Sch 100     |
| 120   | Sch 120     |
| 140   | Sch 140     |
| 160   | Sch 160     |
| XXS   | XXS         |
| 15L   | 150#        |
| 30L   | 300#        |
| 40L   | 400#        |
| 60L   | 600#        |
| 90L   | 900#        |
| 150L  | 1500#       |
| 200L  | 2000#       |
| 250L  | 2500#       |
| 300L  | 3000#       |
| 400L  | 4000#       |
| 600L  | 6000#       |
| 900L  | 9000#       |
+-------+-------------+

但是当我去嵌套它以获得与我相同的结果时......

But when I go to nest this to get the same result I have...

select alpha,description 
from cs_quality 
where class in (select class from cs_item where code = "007")

+-------+-------------+
| alpha | description |
+-------+-------------+
| STD   | STD         |
| XS    | XS          |
| 5     | Sch 5       |
| 10    | Sch 10      |
| 20    | Sch 20      |
| 40    | Sch 40      |
| 60    | Sch 60      |
| 80    | Sch 80      |
| 100   | Sch 100     |
| 120   | Sch 120     |
| 140   | Sch 140     |
| 160   | Sch 160     |
| XXS   | XXS         |
+-------+-------------+

这只是class in 1"的一部分……它对,3"组件犹豫不决.有没有办法将嵌套的选择解释为文字文本?

Which is just the part of "class in 1"... it balks on the ",3" component. Is there a way for the nested select to be interpreted as literal text?

谢谢大家，非常感谢.我在表述这个问题时遇到了一些麻烦，但会根据需要进行编辑.

Thanks all, much appreciated. I had a bit of trouble wording this question but will edit as needed.

推荐答案

规范化、规范化、规范化你的表，在本例中是表 cs_item.您不应在一个字段中存储多个(逗号分隔)值.

Normalize, normalize, normalize your tables, in this case table cs_item. You should NOT store multiple (comma separated) values in one field.

在你这样做之前，你可以使用:

Until you do that, you can use:

select alpha, description 
from cs_quality 
where FIND_IN_SET( class , (select class from cs_item where code = '007'))

或

select q.alpha, q.description 
from cs_quality AS q
  join cs_item AS i
    on FIND_IN_SET( q.class , i.class )
where i.code = '007'

但是这种对 JOIN 使用特殊函数而不是相等的方法会导致查询速度非常慢.存储逗号分隔的列表会导致大量其他问题.看这里:

But this kind of using special functions instead of equality for JOINs, leads to very slow queries. Storing comma separated lists leads to a ton of other problems. See here:

• 在数据库列中存储逗号分隔列表真的那么糟糕吗?

简短的回答是:是的，很糟糕.

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