Pre-QueryPre-Select in Forms (Difference)

PRE-QUERY fires just before Forms begins to prepare the SQL statement that will be required to query the appropriate records from the database in response to the query criteria that have been entered into the example record.

It is the designer's last chance to "deposit" query criteria into the items in the block as if they had been entered into the example record by the operator.

PRE-SELECT fires after the PRE-QUERY trigger has fired, and just before the actual, physical construction of the SELECT statement begins. It would typically be used in conjunction with an ON-SELECT trigger in which the
designer would be supplanting the normal construction of the SELECT statement with a user exit of his own to construct and prepare the SELECT statement for execution (perhaps against a foreign datasource).