Modify SQL for Standard Layer
If you wish to refine the Select statement for retrieving the data from geometry table then click on the Modify SQL button.
From v5.6.0, if you wish to check that your syntax is correct, you may click the Test SQL button. You should see the following dialog:
Prior to v5.6.4 only
If you add anything to the SQL, for example a WHERE clause, you will need to add 'SELECT * FROM' to the beginning of the query for it to be valid.