'better' SQL to return results faster from the sample button in the query builder

[rhys.stewart@…]

Currently the sql that is used to return a subset of the values of a given column is:

SELECT DISTINCT mycolumn FROM mytable ORDER BY mycolumn LIMIT 25

this will be very slow on very large tables. On a table with ~670000 records this took about 15 seconds execute. A faster method would be a subselect as follows:

SELECT DISTINCT mycol from (SELECT mycol FROM mytable LIMIT 5000) as myfoo

This query took much less than a second to execute on the same table.

QgsPgQueryBuilder::on_btnSampleValues_clicked()

[g_j_m]

Applied in svn r6032

Thanks for the improvement.

[(none)]

Milestone Version 0.8 deleted