Messing With Statistics

Erik Darling shows how to fake stats:

One thing I’ve found is that the inflated counts don’t seem to change anything for Identities, or Primary Keys. You’ll always get very reasonable plans and estimates regardless of how high you set row and page counts for those. Regular old clustered indexes are fair game.

Some really interesting things can start to happen to execution plans when SQL thinks there’s this many rows in a table. The first is that SQL will use a rare (in my experience) plan choice: Index Intersection. You can think of this like a Key Lookup but with two nonclustered indexes rather than from one nonclustered index to the clustered index.

This is very useful when you don’t have many rows in dev, can’t put many rows in dev, and can’t restore a stats-only database from prod.

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Statistics and Multiple Single-Column Indexes

Erik Darling is fusing together queries like Dr. Frankenstein in his lab: You may have noticed that both queries get pretty bad estimates. You might even be thinking about leaving me a comment to update stats. The thing is that I created these indexes, which means they get stats built with a full scan, and […]

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Explaining Column Statistics

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