SQL-仅当B不存在时选择A

Question

I have this SQL statement (modified, because the real query is huge):

select tblInfo.IDNum, tblAddress.PrimaryAddress
from tblInfo
join tblAddress
on tblInfo.Agent = tblAddress.Agent
where (some stuff)

And I get a table that looks roughly like this:

|| IDNum || PrimaryAddress ||
-----------------------------
|| 01234 || 1              ||
|| 23456 || 1              ||
|| abcde || 0              ||
|| abcde || 1              ||
|| zyxwv || 0              ||

I need a way to return all records that have a PrimaryAddress of 1, as well as all records that have a PrimaryAddress of 0 and don't have an IDNum already returning the PrimaryAddress of 1. ie In the above example, (abcde || 0) should be excluded because (abcde || 1) exists.

Answer 1

Use NOT EXISTS

SELECT tblInfo.IDNum, tblAddress.PrimaryAddress
FROM tblInfo
INNER JOIN tblAddress
    ON tblInfo.Agent = tblAddress.Agent
WHERE tblAddress.PrimaryAddress = 1
OR  ( tblAddress.PrimaryAddress = 0 AND NOT EXISTS
    (
       SELECT 1 FROM tblInfo t2 INNER JOIN tblAddress a2 ON t2.Agent = a2.Agent
       WHERE t2.IDNum = tblInfo.IDNum AND a2.PrimaryAddress = 1
    )
)

Answer 2

In this case, a simple GROUP BY should work for what you are trying to do. Effectively you are saying you want all IDNum values to appear once, with the PrimaryAddress value corresponding to the highest value (1 if it exists, 0 if it doesn't).

Assuming you need to preserve your original query because you're doing other work with it, you could use:

SELECT IDNum, MAX(PrimaryAddress) AS PrimaryAddress
FROM
(
    select tblInfo.IDNum, tblAddress.PrimaryAddress
    from tblInfo
    join tblAddress
    on tblInfo.Agent = tblAddress.Agent
    where (some stuff)
)
GROUP BY IDNum

This should work in MS SQL Server and Oracle, not sure about other DBMSs. If the nested query doesn't work in the DBMS you're using, you should be able to populate a temporary table with the results of your first query, then perform the grouping against that table.

Answer 3

I hope this helps

select * from tblAddress mainTBL
where mainTBL.primaryaddress = (Case when EXISTS(select t1.IDNUM from tblAddress t1 where
           mainTBL.IDNUM = t1.IDNUM AND t1.primaryAddress = 1)  THEN 1 ELSE 0 END)

Check the SQL fiddle