Re: Index use difference betweer LIKE, LIKE ANY?

On Sun, Feb 27, 2011 at 2:43 AM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:

> On 2/25/11 5:31 AM, Sam Wong wrote:
> > I found that "LIKE", "= ANY (...)", "LIKE .. OR LIKE .." against a text
> > field used the index correctly, but not "LIKE ANY (...)". Would that be a
> > bug?
>
> No, it would be a TODO. This is a known limitation; it needs some
> clever code to make it work, and nobody's written it.
>
>
came up with attached patch without thinking too much.
With this patch, the explain output for the same query is as below:

postgres=# explain select * from shipment_lookup where (UPPER(lookup)
LIKE
ANY(ARRAY['SD1102228482%', 'ABCDEFGHIJK%']))
;e
QUERY
PLAN
-------------------------------------------------------------------------------------------------
Seq Scan on shipment_lookup (cost=0.00..254057.36 rows=2000 width=14)
* Filter: ((upper(lookup) ~~ 'SD1102228482%'::text) OR (upper(lookup) ~~
'ABCDEFGHIJK%'::text))*
(2 rows)

postgres-#

The thing to be noted here is that the where clause "<pred> LIKE ANY
ARRAY[..]"
has been converted into
(<pred> LIKE first_array_element) or (<pred> LIKE second_array_element) or
....

Please pass on your inputs.

Regards,
Chetan

--
Chetan Sutrave
Senior Software Engineer
EnterpriseDB Corporation
The Enterprise PostgreSQL Company
Phone: +91.20.30589523

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