SQL Server IIF vs CASE

问题:

I recently came to know about the availability of IIF function in SQL Server 2012. I always use nested CASE in my queries. I want to know the exact purpose of the IIF statement and when should we prefer using IIF over CASE Statement in the query. I mostly use nested CASE in my queries.

Thanks for all the inputs.

回答1:

IIF is the same as CASE WHEN <Condition> THEN <true part> ELSE <false part> END. The query plan will be the same. It is, perhaps, "syntactical sugar" as initially implemented.

CASE is portable across all SQL platforms whereas IIF is SQL SERVER 2012+ specific.

回答2:

IIF is a non-standard T-SQL function. It was added to SQL SERVER 2012, so that Access could migrate to SQL Server without refactoring the IIF's to CASE before hand. Once the Access db is fully migrated into SQL Server, you can refactor.