The uniquifier is a hidden 4-byte value that SQL Server adds to duplicate keys in a non-unique clustered index. This post measures its real cost row by row on SQL Server 2025 and shows it on the page. It also compares it with a unique key you choose yourself.
What Happens If the Clustered Index is Disabled? – Interview Question of the Week #291
Question: What Happens If the Clustered Index is Disabled?
Answer: If you disable the clustered index, you can’t retrieve data from the table.
How to Force Index on a SQL Server Query? – Interview Question of the Week #281
Question: How to Force Index on a SQL Server Query?
Answer: I personally do not like to force an index on any query. Let us learn together.
Index Design Rules: Ten Don’ts and Where They Break
These index design rules came from a client’s list of ten index don’ts, and readers argued with several of them. This post turns the checkable rules into read-only queries on a demo database, and it measures what each rule really costs. The rest are warnings, not laws, and the post says which is which.
SQL SERVER – Heaps, Scans and RID Lookup
The question was do heaps are very bad and always force a table scan? Let us learn about RID Lookup, Heaps and table scan.
RID Lookups on Heaps vs Key Lookups on Clustered Tables
Compare RID lookups on heaps with clustered key lookups, inspect forwarded records, and test covering indexes with actual plans and reads.
NEWID vs NEWSEQUENTIALID: What Each Does to Your Index
NEWID vs NEWSEQUENTIALID decides whether new uniqueidentifier keys land at random in your clustered index or in order at the end. This post loads 20,000 rows with each default, measures pages, fullness and fragmentation, and shows the limits of NEWSEQUENTIALID. It also answers what happens when you switch the default on a table that already has rows.