Re: OPtimize the performance of a query

[Melvin Davidson <melvin6925@xxxxxxxxx>]

On Tue, Jan 16, 2018 at 11:46 AM, James Keener <jim@xxxxxxxxxxxxx> wrote:

Do you have any indecies? https://www.postgresql.org/docs/current/static/indexes-expressional.html might be helpful to you.

Also, EXPLAIN will help you understand how your query is being run and where it can be improved.

https://www.postgresql.org/docs/current/static/using-explain.html

http://postgresguide.com/performance/explain.html

http://jimkeener.com/posts/explain-pg

 

Jim

On Tue, Jan 16, 2018 at 11:32 AM, hmidi slim <hmidi.slim2@xxxxxxxxx> wrote:

Hi,

I have two tables in the same database: geoname and test_table.

The geoname table contains many columns which are: name, feature_class, feature_code, admin1, admin2,admin3, name and so on.

The second table 'test_table' contains only the columns: city, state.

There is no join between the two tables and I want to make a match between the data contained in each of them because I need the result for a farther process.

I wrote this query:

select g.name, t.city

from geoname as g, test_table as t

where (lower(g.feature_class) like 'P' or lower(g.feature_class) like 'L')

and lower(g.country_code) like 'US'

and lower(g.admin1) like lower(t.state)

and (lower(g.name) like lower(t.city) or lower(g.name) like lower(t.city || 'city'))

The table geoname contains 370260 rows and the table test_table contains 10270 rows.

The query took a long time to accomplish more than half an hour.Should I add another column in the table test_table which contains the country_code and make an inner join with the geoname table or should I use indexs to accelerate the process?

It would have been more helpful if you had included
the actual table structures for both tables.
However, I would start by creating separate indexes on
lower(feature_class)
lower(country_code)
lower(admin1)
lower(name)
lower(city)

That being said, you are better off forcing lowercase on all fields
BEFORE inserting into the table.
EG:

INSERT INTO test_table VALUES (lower(some_key), lower(name), lower(feature_class), ....)

Then you would would not need to use lower() in the indexes or the query.

Please, in the future, always include your version of PostgreSQL and O/S

--

Melvin Davidson
I reserve the right to fantasize.  Whether or not you
wish to share my fantasy is entirely up to you.