IIF 'Incorrect syntax near' error at SQL Server 2014

Question

I am trying date control by month with this script

DECLARE @Date DATETIME = '2015-07-31';
DECLARE @MonthCount INT = 3;
DECLARE @controlDate DATETIME = '2015-04-28';

SELECT
    MONTH(@controlDate),
    MONTH(DATEADD(MONTH, -@MonthCount, @Date)),
    IIF(MONTH(@controlDate) > MONTH(DATEADD(MONTH, -@MonthCount, @Date)),'OK','No') as isOK     

But I am getting this syntax error:

Msg 102, Level 15, State 1, Line 8 Incorrect syntax near '>'

EDIT: When I try if it is working:

DECLARE @Date DATETIME = '2015-07-31';
DECLARE @MonthCount INT = 3;
DECLARE @controlDate DATETIME = '2015-04-28';

if(MONTH(@controlDate) > MONTH(DATEADD(MONTH, -@MonthCount, @Date)))
print 'OK'
else
print 'No'

What am I doing wrong or is this a bug?

Answer 1

This happens when you're not running on a correct version of SQL Server, or if the compatibility level of the database isn't set sufficiently.

To check compatibility level:

select compatibility_level 
from sys.databases 
where name = '<database name>'

To alter compatibility level:

alter database <database-name> 
set compatibility level = 110 -- SQL Server 2012

List of compatibility levels: https://msdn.microsoft.com/en-us/library/bb510680.aspx