Re: Unique index problem

____________________________________
 pgsql-general-owner@postgresql.org [pgsql-general-owner@postgresql.org]" im Auftrag von "Scott Marlowe
[scott.marlowe@gmail.com]
ndet: Sonntag, 20. Dezember 2015 17:02
Sterpu Victor
PostgreSQL General
eff: Re: [GENERAL] Unique index problem

un, Dec 20, 2015 at 9:00 AM, Scott Marlowe <scott.marlowe@gmail.com> wrote:
 Sun, Dec 20, 2015 at 8:50 AM, Sterpu Victor <victor@caido.ro> wrote:
ello

>>> I created a unique index that doesn't seem to work when one column is NULL.
>>> Index is created like this: CREATE UNIQUE INDEX lab_tests_groups_siui_uni ON
>>> lab_tests_groups_siui(id_lab_tests_siui, id_lab_tests_groups, valid_from,
>>> id_lab_sample_types);
>>> Now I can run this insert twice and I will have 2 records in the database
>>> that seem to violate this index:
>>> INSERT INTO lab_tests_groups_siui(id_lab_tests_siui, id_lab_tests_groups,
>>> valid_from) VALUES(463, 9183, '2014-06-01');
>>>
>>> When I create the index like this "CREATE UNIQUE INDEX
>>> lab_tests_groups_siui_uni ON lab_tests_groups_siui(id_lab_tests_siui,
>>> id_lab_tests_groups, valid_from);" index works fine.
>>>
>>> I tested this on postgres 9.1.4 and 9.1.9.
>>
>> This is normal operation, as one NULL is unique from other NULLS, as
>> far as the db is concerned. If you want it to work some other way, you
>> need to use a value other than null, or make an index that's something
>> like un


Hello,

> CREATE UNIQUE INDEX lab_tests_groups_siui_uni ON lab_tests_groups_siui(id_lab_tests_siui, id_lab_tests_groups,
valid_from,id_lab_sample_types); 

assuming that only id_lab_sample_types can be null, you could cover this with 2 partial indexes:

CREATE UNIQUE INDEX lab_tests_groups_siui_uni_a ON lab_tests_groups_siui(id_lab_tests_siui, id_lab_tests_groups,
valid_from)WHERE (id_lab_sample_types IS NULL); 
and
CREATE UNIQUE INDEX lab_tests_groups_siui_uni_b ON lab_tests_groups_siui(id_lab_tests_siui, id_lab_tests_groups,
valid_from,id_lab_sample_types) WHERE (id_lab_sample_types IS NOT NULL); 

There is a serious caveat though: queries that don't contains a "id_lab_sample_types IS [NOT] NULL" condition will
ignorethe index. 

Maybe there is also a way using DISTINCT(id_lab_tests_siui, id_lab_tests_groups, valid_from, id_lab_sample_types) in
theindex definition,  but I've never tried that and suspect the planner will also have trouble to include such an index
inthe plan. 

regards,

Marc Mamin