Greg Stark wrote:
If Postgres used an index it would call odd(), which would return 1 because
it's the first time, and then Postgres would go look up the rows where col is
1 and return all of them. That's a very different behaviour from if the index
isn't used. If all the records have col=1 then you're getting all of the
records instead of half of them. If col=0 then you're getting none of them
instead of half of them.
This is the differance between "volatile" and "stable" functions, but
not the answer to why an index lookuo are per query and not per row, is
it not ?
/BL
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