Question

Tables structure are below :

Table1 (ID int, value1 int,...)

ID       Value1
----    --------
1        10
2        20
5        12


Table2 (ID int, value2 int,...)

ID       Value2
----    --------
1        13
3        24
4        11


Table3 (ID int, value3 int,...)
ID       Value3
----    --------
4        150
5        100

My expected output is below.

ID       Value1        Value2        Value3
----    --------      --------      --------
1         10            13             NULL
2         20            NULL           NULL
3         NULL          24             NULL
4         NULL          11             150
5         12            NULL           100

It should be noted that above tables is huge and I want to have best performance.

My query suggestion is below :

Select ID, 
       SUM(Value1) AS Value1, 
       SUM(Value2) AS Value2,
       SUM(Value3) AS Value3 
From (
    Select ID, Value1 , NULL as value2, NULL as value 3
    From Table1

    Union ALL

    Select ID, NULL , value2, NULL
    From Table2

    Union ALL

    Select ID, NULL, NULL, value 3
    From Table3
    )Z
Group By Z.ID

Answer 1

Assuming you only have one value per id, this should do the trick:

SELECT aux.ID, t1.Value1, t2.Value2, t3.Value3
FROM 
(SELECT ID FROM Table1
 UNION
 select ID FROM Table2
 UNION
 SELECT ID FROM Table3) aux
LEFT OUTER JOIN Table1 t1 ON aux.ID = t1.ID
LEFT OUTER JOIN Table2 t2 ON aux.ID = t2.ID
LEFT OUTER JOIN Table3 t3 ON aux.ID = t3.ID

---

If you’ve more than one value:

SELECT aux.ID, SUM(t1.Value1) as 'Value1', SUM(t2.Value2) as 'Value2', SUM(t3.Value3) as 'Value3'
FROM 
(SELECT ID FROM Table1
 UNION
 select ID FROM Table2
 UNION
 SELECT ID FROM Table3) aux
LEFT OUTER JOIN Table1 t1 ON aux.ID = t1.ID
LEFT OUTER JOIN Table2 t2 ON aux.ID = t2.ID
LEFT OUTER JOIN Table3 t3 ON aux.ID = t3.ID
GROUP BY aux.ID