On 20 August 2013 11:46, Jani Tiainen wrote:

I think pretty latest PostgreSQL can use indexes to filter NULL values as well (doesn't have facility to store them though).
Postgres can use an index to find NULL values, so SELECT * FROM foo
WHERE col IS NULL can be indexed.

Not sure what you mean by "doesn't have facility to store them". NULL
values are stored in the database, they just don't occupy the same
space as non-NULL values. PostgreSQL's support of NULL values is full
and complete, in line with SQL Standard requirements.
MySQL uses table statistics to determine are NULL values indexed or not.
Postgres stats include number of values NULL.

  Simon Riggs http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services

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postedAug 19, '13 at 7:39a
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