On 2020-05-14 16:32:41 +0400, otar shavadze wrote: > also nor index drop is an option, because I need re-create index as I use this > table in procedure, so index is necessary for further queries. So total > runtime will not decreased.
A full index on a column where all the values are the same (NULL in this
case) is useless. For querys which check for the existing value, the
optimizer will notice that a full table scan is faster. For query which
use any other value, you expect 0 results: So all the optimizer want to know is
that the value is indeed not in the column so that it can skip the table
entirely. You can do that with a partial index (WHERE col IS NOT NULL)
or maybe even a constraint.
So I would drop the full index, update the table and then create a
partial index.
hp
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