MySQL获取行仅包含具有特定值的行

Question

Lets say, my tables has the following rows:

  id | prop1 | prop2 
______________________
  1    foo      a
  2    bar      a
  3    foo      b
  4    bar      b
  5    foo      c

Now in this case, i want to get rows grouped by prop1 but ignore the groups that don't contain a row with prop2=c

So the intended result is:

1 foo a
3 foo b
5 foo c

Note, now there is only one group in the example but i want to be able to get all of them. How can i achieve this approach?

Answer 1

Your expected result is not grouped by prop1 . If it was grouped by prop1 then you would get only one record in the result.

To achieve the above, we can write a simple SELECT with sub-query, eg:

SELECT *
FROM table
WHERE prop1 IN (
 SELECT prop1 FROM table WHERE prop2 = 'c'
);

Answer 2

You can use exists clause to remove all the rows if it does not have prop2 = c using below query.

select * 
from your_table t1
where 
exists (select 1 from your_table t2 where t1.prop1 = t2.prop1
        and t2.prop2 = 'c')

Explaination: Exists caluse will return true if it finds c for that group else false.

Answer 3

The following query fetches all record with prop2 = 'c' (T1) and joins them on all records (T2) that have an equal prop1:

select T2.*
from    TABLE T1
join TABLE T2 ON T1.prop1=T2.prop1
WHERE T1.prop2 = 'c'
GROUP BY id

Answer 4

SELECT * FROM table WHERE prop2 != "c" GROUP BY prop1

该行将删除带有C的att行，并在prop1上将所有其他内容分组