The PostgreSQL 9.0 Reference Manual - Volume 3 - Server Administration Guide by The PostgreSQL Global Development Group Paperback (6"x9"), 274 pages ISBN 9781906966072 RRP £9.95 ($14.95) Sales of this book support the PostgreSQL project! Get a printed copy>>>

PostgreSQL 9.0 Reference Manual Volume 3 Buy the book here! >>> support free documentation

4.12.2 Platform and Client Compatibility

transform_null_equals (boolean)

When on, expressions of the form expr = NULL (or NULL = expr) are treated as expr IS NULL, that is, they return true if expr evaluates to the null value, and false otherwise. The correct SQL-spec-compliant behavior of expr = NULL is to always return null (unknown). Therefore this parameter defaults to off. However, filtered forms in Microsoft Access generate queries that appear to use expr = NULL to test for null values, so if you use that interface to access the database you might want to turn this option on. Since expressions of the form expr = NULL always return the null value (using the SQL standard interpretation), they are not very useful and do not appear often in normal applications so this option does little harm in practice. But new users are frequently confused about the semantics of expressions involving null values, so this option is off by default. Note that this option only affects the exact form = NULL, not other comparison operators or other expressions that are computationally equivalent to some expression involving the equals operator (such as IN). Thus, this option is not a general fix for bad programming. Refer to Volume 1A: 7.2 Comparison Operators for related information.