conditional joins in select statement

  • SELECT t1.id,name, from table1 t1 INNER join table t2 on t1.id=t2.pid

    case when type='A' then

    Inner join table3 t3 on t1.id=t3.id

    else

    Inner join table4 t4 on t1.id=t4.id

    END

  • That's not possible in SQL.

    You need to write two seperate queries and choose between them using an IF statement, or you construct your query dynamically and execute it with sp_executesql.

    Need an answer? No, you need a question
    My blog at https://sqlkover.com.
    MCSE Business Intelligence - Microsoft Data Platform MVP

  • As Koen mentioned that is not possible in SQL and should explore the options he mentioned.

    Probably one more option if i understand your question correctly is to do a LEFT JOIN as below. Try if this helps...

    SELECT T1.Id,T2.Name,

    CASE WHEN T1.Type = 'A' THEN T3.SomeColumn

    ELSE T4.SomeColumn

    END AS SomeColumn

    FROM Table1 AS T1

    INNER JOIN Table2 AS T2 ON T1.Id = T2.Pid

    LEFT OUTER JOIN Table3 AS T3 ON T1.Id = T3.Id AND T1.Type = 'A'

    LEFT OUTER JOIN Table4 AS T4 ON T1.Id = T4.Id AND T1.Type <> 'A'

  • Perhaps something like this might work for you:

    SELECT t1.id,name

    FROM table1 t1

    INNER JOIN table t2 ON t1.id=t2.pid

    INNER JOIN table3 t3 on t1.id=CASE type WHEN 'A' THEN t3.id ELSE t1.id END

    INNER JOIN table4 t4 on t1.id=CASE type WHEN 'A' THEN t1.id ELSE t4.id END


    My mantra: No loops! No CURSORs! No RBAR! Hoo-uh![/I]

    My thought question: Have you ever been told that your query runs too fast?

    My advice:
    INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
    The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.

    Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
    Since random numbers are too important to be left to chance, let's generate some![/url]
    Learn to understand recursive CTEs by example.[/url]
    [url url=http://www.sqlservercentral.com/articles/St

Viewing 4 posts - 1 through 3 (of 3 total)

You must be logged in to reply to this topic. Login to reply