Mysql：从一个表中选择数据，在表2中，表2中的值必须全部为0

Question

I want to be able to select everything from t1 where t1.active = 1 where the ID also exists in t2 and t2.active = 0

But I don't want to show any entry in t1 for an ID if the entries that match in t2 have 1 entry where t2.active = 1

Example:

Table 1
-----------
t1id|Active|
1 | 1 |  
2 | 1 | 



Table 2
-----------
t2id|Active|
1 | 0 |  
1 | 0 |  
1 | 1 |  
2 | 0 |  
2 | 0 |  

Should give the result of:

t1id|Active| 
2 | 1 | 

I've tried:

SELECT * FROM t1 WHERE t1.active = 1  
AND EXISTS(SELECT * FROM t2 WHERE t2.id = t1.id  
AND t2.active = 0  
GROUP BY t2.id, t2.active HAVING COUNT(t2.id) > 1 AND t2.active = 0)

Unfortunately this still returns entries from t1 where the id exists in t2 and has one entry where active = 1

Any help would be appreciated!

Answer 1

I see two solutions.

1 short, using max

SELECT * 
FROM t1 
WHERE 
  t1.active = 1 AND 
  EXISTS(SELECT null 
         FROM t2 WHERE t2.id = t1.id
         GROUP BY t2.id 
        --if the max active = 0 then it means there's no t2.active = 1
        HAVING MAX(t2.active) =0)

One less elegant in code, but probably clearer to explain what you try to achieve

SELECT * FROM t1 
WHERE 
    t1.active = 1 AND
    EXISTS (    SELECT null FROM t2 
                WHERE t2.id = t1.id
                AND t2.active = 0) AND
    NOT EXISTS (SELECT null FROM t2 
                WHERE t2.id = t1.id
                AND t2.active = 1)

Answer 2

Why don't you try using INNER JOIN?

The Query must be like that:

select * 
from T1 a
LEFT JOIN T2 b 
ON a.ID = b.ID
and b.ACTIVE = (select max(active) from T2 group by ID)
where a.ACTIVE= 1
b.ACTIVE = 0