Question

I need to be able create a unique constraint that checks that a string and integer combination is unique.

I have tried code:

ALTER TABLE mytable ADD CONSTRAINT
constraint_Unique_ForeignID_MyString UNIQUE NONCLUSTERED
(
     foreign_id, my_string_col
)

But I get error:

Msg 1919, Level 16, State 1, Line 1
Column ‘my_string_col’ in table
‘my_string_tbl’ is of a type that is
invalid for use as a key column in an
index.
Msg 1750, Level 16, State 0, Line 1
Could not create constraint.
See previous errors.

How can I create the constraint I need?

Answer 1

How BIG of a VARCHAR is your column??

Any index can only contain columns up to a maximum of 900 bytes total. There is no way to get around this, or to increase that number to a higher value.