On 06/20/2012 09:11 AM, Craig Ringer wrote:
For those of us who don't know MS-SQL, can you give a quick explanation of what the INCLUDE keyword in an index definition is expected to do, or some documentation references?
He's talking about what MS SQL Server commonly calls a "covering index." In these cases, you can specify columns to be included in the index, but not actually part of the calculated hash. This prevents a trip to the table data, so selects can be serviced entirely by an index scan.
PostgreSQL is about half way there by allowing index-only scans, though I've no idea if they intend on adding further functionality like this. Effectively you can trade index bloat for query speed. But considering the differences between the engines, it might not be necessary. I couldn't say.
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