带有“where in”子句的嵌套 MySql Select 语句

Question

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.

Ie

select class 
from cs_item 
where code="007"

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

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#       |
+-------+-------------+

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         |
+-------+-------------+

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?

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

Answer 1

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

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'))

or

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'

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:

• Is storing a comma separated list in a database column really that bad?

Short answer is: Yeah, it's that bad .

Answer 2

Your query needs to return multiple rows like this:

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

Or else it is as if you are doing:

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

Which you do not want.

Answer 3

Better use join , instead of a nested query