UNION ALL Sql query - how to bind three tables
Question
I have the following tables:
T1
ID PRIORITY
1 1
2 1
3 2
4 4
T2
ID SERVICE
1 PSTN
1 ADSL
3 ADSL
T3
ID DEVICE
1 BSC1
3 BSC7
4 BSC7
I want as output
ID PRIORITY SERVICE/DEVICE
1 1 PSTN
1 1 ADSL
1 1 BSC1
2 1
3 2 ADSL
3 2 BSC7
How to bind those tables using UNION ALL? Also I must put WHERE clause for T1 WHERE PRIORITY!=4
Total number in output table for one id should be the summary of T2+T3 (FOR ID=1 2+1=3) but for ID=2 it also SHOULD exist in table output with blank second column.
Thank you
Solution
If you are okay using just a UNION
and not UNION ALL
this should give you what you want
SELECT t1.Id, t1.Priority, COALESCE(t2.Service, '') AS [Service/Device]
FROM t1
LEFT JOIN t2 ON t1.Id = t2.Id
WHERE t1.Priority != 4
UNION
SELECT t1.Id, t1.Priority, COALESCE(t3.Device, '') AS [Service/Device]
FROM t1
LEFT JOIN t3 ON t1.Id = t3.Id
WHERE t1.Priority != 4
OTHER TIPS
select T1.id , T1.PRIORITY ,T2.SERVICE as service/Device from t1
left outer join T2 on T2.id=T1.id where T1.PRIORITY!=4
union all
select T1.id , T1.PRIORITY ,T3.DEVICE as service/Device from t1
left outer join T3 on T3.id=T1.id where PRIORITY!=4
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