Msg 3745, Level 16, State 1, Line 1
Only a clustered index can be dropped online.
This error message appears when you try to drop a nonclustered index online.
The T-SQL statement can be parsed, but causes the error at runtime.
Errors of the Severity Level 16 are generated by the user and can be fixed by the SQL Server user. The statement cannot be executed this way. You cannot drop a nonclustered index online.
This error message was introduced with SQL Server 2005.
IF OBJECT_ID(‘tempdb..#t’) > 0
DROP TABLE #t
CREATE TABLE #t
CREATE UNIQUE NONCLUSTERED INDEX IX_t_id ON #t(id)
DROP INDEX IX_t_id
WITH (ONLINE = ON);
In the above example we try to drop the nonclustered index IX_t online. This raises the error.