The condition in an app engine DO-WHILE contruct is true if the associated SQLSELECT statement returns any rows. Any subsequent action executes until the SQL statement doesn't return any more rows.
In contrast, the DO-UNTIL construct executes the actions first and then runs the SQL. The condition is true if the SQL statement returns any row and terminates the loop.
DO-SELECT executes the actions for each row returned by the SQL statement. It is like a 'FOR LOOP'.
DO-WHEN is like an 'IF Statement'. If the SQL returns a row, then the actions are executed, otherwise they're skipped.
In contrast, the DO-UNTIL construct executes the actions first and then runs the SQL. The condition is true if the SQL statement returns any row and terminates the loop.
DO-SELECT executes the actions for each row returned by the SQL statement. It is like a 'FOR LOOP'.
DO-WHEN is like an 'IF Statement'. If the SQL returns a row, then the actions are executed, otherwise they're skipped.
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