在另一个SQL查询中使用GROUP_CONCAT的结果

Question

I need to use the results contained in a GROUP_CONCAT in another query but i can't work out how to do this as they are in a comma separated list.

For example, if GROUP_CONCAT(sample) contained a,b,c,d,e,f I tried to do

SELECT * FROM `orders` WHERE `this` IN GROUP_CONCAT(sample)

but i get a syntax error.

I can't use

 WHERE `this` = GROUP_CONCAT(sample)

because that tries to match this to the comma separated list

Is there a specific method to achieve this?

Answer 1

Use FIND_IN_SET

SELECT * FROM `orders` WHERE FIND_IN_SET(`this`, GROUP_CONCAT(sample))

Or You can use (if there is no special reason to use GROUP_CONCAT )

SELECT * FROM `orders` WHERE `this` IN (sample)

if sample is the column of orders table

Answer 2

You should just combine the two queries:

SELECT *
FROM `orders`
WHERE exists (select 1
              from <other query without aggregation> s
              where this = s.sample
             )

This query can be optimized. You can write:

select *
from orders o
where find_in_set(o.this, sample) > 0;

This has to use a full table scan and cannot take advantage of an index.