WHERE clause limitations

The sysams system catalog table has no indicator to inform the database server that a secondary access method cannot process complex qualifications. If the access method does not process the Boolean operators in a WHERE clause, perform the following actions:

• Provide examples in the user guide of UNION and subqueries that replace AND or OR operators in a WHERE clause, as the following example demonstrates.

  Query using boolean operator	Query using UNION
  SELECT * FROM videos WHERE title = 'Hamlet' OR year > 1980;	SELECT * FROM videos WHERE title = 'Hamlet UNION SELECT * FROM videos WHERE year > 1980;

• In the am_scancost purpose function, call the mi_qual_issimple() or mi_qual_boolop() accessor function to detect a Boolean operator.

  If mi_qual_issimple() returns MI_FALSE, for example, return a value that forces the optimizer to ignore this access method for the particular query.

• Raise an error if mi_qual_issimple() returns MI_FALSE to the am_getnext purpose function.