Working with null Values

авторPosted by Jon Gabrielson on December 18 2002 4:27pm [Delete] [Edit]


The function 'COALESCE' can simplify working with null
values.
for example, to treat null as zero, you can use:
select COALESCE(colname,0) from table where
COALESCE(colname,0) > 1;

in a date field, i used:
ORDER BY
(coalesce(TO_DAYS(date),TO_DAYS(CURDATE()))-TO_DAYS(CURDATE()))
to treat NULL as the current date.





Posted by Bob Kolk on January 10 2003 12:05pm [Delete] [Edit]

Use IFNULL() in your SELECT statement is make the NULL any value you wish.

IFNULL(expr1,expr2)
If expr1 is not NULL, IFNULL() returns expr1, else it returns expr2. IFNULL() returns a numeric or string value, depending on the context in which it is used:
mysql> SELECT IFNULL(1,0);
-> 1
mysql> SELECT IFNULL(NULL,10);
-> 10
mysql> SELECT IFNULL(1/0,10);
-> 10
mysql> SELECT IFNULL(1/0,'yes');
-> 'yes'