CODEWITHSUNDEEP
sql-server
Émile Bélair
Émile Bélair

Reputation: 1

Make a SQL Server JOIN on a specific condition

I am a complete beginner with SQL, and I have to turn a query like this one:

SELECT col1, col2, col3 FROM  db1
LEFT OUTER JOIN  (SELECT col1, col2 FROM db2 WHERE some_conditions) AS query1
  ON (query1.col1 = col2)

Into a query like this one:

SELECT col1, col2, col3 FROM db1
if col1 = 1
LEFT OUTER JOIN  (SELECT col1, col2 FROM db2 WHERE some_conditions) AS query1
  ON (query1.col1 = col2) 
else
LEFT OUTER JOIN  (SELECT col1, col2 FROM db2 WHERE some_other_conditions) AS query1
  ON (query1.col1 = col2)

But the latter obviously doesn't work in SQL Server. What would be the proper format for a query like this?

Upvotes: 0

Views: 70

Answers (1)

Andomar
Andomar

Reputation: 238048

You could use a complex on clause:

select  *
from    db1
left join
        db2
on      db1.col1 = db2.col2
        and (
            (db1.col1 = 1 and some_conditions)
            or (db1.col1 <> 1 and some_other_conditions)
        )

Using or, you can use one codition set in one case, and another condition set in another case.

Upvotes: 1

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