- •Firebird Null Guide
- •Table of Contents
- •Introduction
- •What is NULL?
- •NULL in expressions
- •Expressions returning NULL
- •NULL in boolean expressions
- •More logic (or not)
- •NULL in aggregate functions
- •NULL handling in UDFs
- •NULL <-> non-NULL conversions you didn't ask for
- •Being prepared for undesired conversions
- •More on UDFs
- •NULL in if statements
- •Testing if something is NULL
- •Setting a field or variable to NULL
- •Dealing with NULLs
- •Testing for NULL - if it matters
- •Finding out if fields are the same
- •Finding out if a field has changed
- •Substituting NULL with a value
- •The COALESCE function
- •Firebird 1.0: the *NVL functions
- •Summary
- •Document history
- •License notice
Firebird Null Guide
NULL behaviour and pitfalls in Firebird SQL
Paul Vinkenoog
15 April 2005 - Document version 0.2
Table of Contents |
|
Introduction ...................................................................................................................... |
3 |
What is NULL? ................................................................................................................. |
3 |
NULL in expressions ......................................................................................................... |
3 |
Expressions returning NULL ...................................................................................... |
4 |
NULL in boolean expressions .................................................................................... |
4 |
More logic (or not) .................................................................................................... |
5 |
NULL in aggregate functions ..................................................................................... |
6 |
NULL handling in UDFs .................................................................................................... |
6 |
NULL <-> non-NULL conversions you didn't ask for .................................................. |
6 |
Being prepared for undesired conversions ................................................................... |
7 |
More on UDFs .......................................................................................................... |
7 |
NULL in if statements ....................................................................................................... |
8 |
Testing if something is NULL ............................................................................................ |
8 |
Setting a field or variable to NULL ..................................................................................... |
9 |
Dealing with NULLs ......................................................................................................... |
9 |
Testing for NULL - if it matters .................................................................................. |
9 |
Finding out if fields are the same .............................................................................. |
10 |
Substituting NULL with a value ............................................................................... |
11 |
Summary ........................................................................................................................ |
13 |
A. Document history ........................................................................................................ |
14 |
B. License notice ............................................................................................................. |
15 |
ii