"IN" clause limitation in Sql Server

Question

Does anybody know what is the limit for the number of values one can have in a list of expressions (to test for a match) for the IN clause?

Answer 1

Yes, there is a limit, but MSDN only specifies that it lies "in the thousands":

Including an extremely large number of values (many thousands) in an IN clause can consume resources and return errors 8623 or 8632. To work around this problem, store the items in the IN list in a table.

Looking at those errors in details, we see that this limit is not specific to IN but applies to query complexity in general:

Error 8623:

The query processor ran out of internal resources and could not produce a query plan. This is a rare event and only expected for extremely complex queries or queries that reference a very large number of tables or partitions. Please simplify the query. If you believe you have received this message in error, contact Customer Support Services for more information.

Error 8632:

Internal error: An expression services limit has been reached. Please look for potentially complex expressions in your query, and try to simplify them.

Answer 2

It is not specific but is related to the query plan generator exceeding memory limits. I can confirm that with several thousand it often errors but can be resolved by inserting the values into a table first and rephrase the query as

select * from b where z in (select z from c)  

where the values you want in the in clause are in table c. We used this successfully with an in clause of 1-million values.