SELECT Statements in WHILE and FOR Statements

If you use a SELECT statement in a WHILE or FOR loop, and if you need to enclose it in parentheses, enclose the entire SELECT statement in a BEGIN…END statement block. The SELECT statement in the first WHILE statement in the following example is interpreted as a call to the procedure var1; the second WHILE statement is interpreted correctly:

DEFINE var1, var2 INT;
WHILE var2 = var1
   SELECT col1 INTO var3 FROM TAB -- error, interpreted as call var1()
   UNION
   SELECT co2 FROM tab2;
END WHILE;

WHILE var2 = var1
   BEGIN
      SELECT col1 INTO var3 FROM TAB -- ok syntax
      UNION
      SELECT co2 FROM tab2;
   END
END WHILE;