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Asked: 2026-05-10T20:24:07+00:00

I have a database where one of the common queries is has a where

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I have a database where one of the common queries is has a ‘where blobCol is null’, I think that this is getting bad performance (as in a full table scan). I have no need to index the contents of the blobCol.

What indexes would improve this? Can an index be built on an expression (blobCol is not null) rather than just a column?

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  1. Yes, most DBMSs support it, for instance in PostgreSQL it is

    CREATE INDEX notNullblob ON myTable (blobCol is not NULL);

    It seems that the best you could do on SQL Server though is to create a computed column that, for example, will contain 1 if blob is null and 0 otherwise and create an index over that.

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