Total size of an index or primary key can not exceed 900 bytes

Question

When I try to create UK for 7 columns I get

Total size of an index or primary key can not exceed 900 bytes.

How can I solve this error?

Answer 1

Other than the obvious (changing the size of these 7 columns), there's no setting or similar. You can however enforce this by using triggers to ensure those 7 columns are unique together.

Answer 2

Nothing particularly satisfactory. See this article for some suggestions of how a unique constraint can be enforced on columns over the 900 byte limit.

• CHECKSUM (Possible collisions)
• Triggers (High Overhead and might fail under snapshot isolation)
• HASHBYTES (Less chance of collisions but still possible)