On 2017-04-19 13:25, Martijn Tonies (Upscene Productions) wrote:
Samuel, others,
Perhaps I'm missing something, but I'd be interested in the reasoning
behind this.
For column 'what', it seems you have no index on all values, only
indices with specific values for 'what'.
How does this speed up the search? Will PostgreSQL use those indices,
instead of using a generic index on 'what' and optionally other
columns?
With regards,
Martijn Tonies
Upscene Productions
http://www.upscene.com
That's a "partial index", it only contains records that meet the
requirements of the index definition.
https://www.postgresql.org/docs/9.5/static/indexes-partial.html
Basically; if you create an index on records where 'name = kees' then if
your query contains "where name=kees"
the planner can just load that index and know that the records in that
index will not contain
any other names, saving the need to filter for 'name=kees'
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