Difference between revisions of "ISNULL()"
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Yvonne.milne (Talk | contribs) |
Yvonne.milne (Talk | contribs) |
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==Purpose== | ==Purpose== | ||
| − | Function to specify an alternative value for a null expression | + | Function to test if an expression evaluates to NULL and optionally specify an alternative value for a null expression |
==Syntax== | ==Syntax== | ||
| − | ISNULL(<expr1>, <expr2>) | + | ISNULL(<expr1> [, <expr2>]) |
==See Also== | ==See Also== | ||
| Line 9: | Line 9: | ||
==Description== | ==Description== | ||
| − | The ISNULL() function evaluates the expression in <expr1>, and if the expression | + | The ISNULL() function evaluates the expression in <expr1>, and returns true (.T.) if the expression evaluates to NULL, otherwise false (.F.). If the optional <expr2> is specified, ISNULL() returns the first non-null value: if <expr1> does not evaluate to NULL, the evaluated result is returned, otherwise <expr2> is evaluated and if it does not evaluate to NULL, its evaluated result is returned. If both <expr1> and <expr2> evaluate to NULL, the ISNULL() function returns NULL. |
==Example== | ==Example== | ||
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INSERT INTO nullon (lastname) VALUES ("Smith") | INSERT INTO nullon (lastname) VALUES ("Smith") | ||
SELECT lastname, isnull(firstname,"Unknown") from nullon | SELECT lastname, isnull(firstname,"Unknown") from nullon | ||
| + | SELECT lastname, isnull(firstname) from nullon | ||
</code> | </code> | ||
Revision as of 06:10, 15 April 2013
Contents
Purpose
Function to test if an expression evaluates to NULL and optionally specify an alternative value for a null expression
Syntax
ISNULL(<expr1> [, <expr2>])
See Also
COALESCE(), EMPTY(), IFNULL(), ISALPHA(), ISBLANK(), ISDIGIT(), NVL(), SET NULL, SET NULLDISPLAY
Description
The ISNULL() function evaluates the expression in <expr1>, and returns true (.T.) if the expression evaluates to NULL, otherwise false (.F.). If the optional <expr2> is specified, ISNULL() returns the first non-null value: if <expr1> does not evaluate to NULL, the evaluated result is returned, otherwise <expr2> is evaluated and if it does not evaluate to NULL, its evaluated result is returned. If both <expr1> and <expr2> evaluate to NULL, the ISNULL() function returns NULL.
Example
set null on CREATE TABLE nullon (firstname c(20), lastname c(20)) INSERT INTO nullon (lastname) VALUES ("Smith") SELECT lastname, isnull(firstname,"Unknown") from nullon SELECT lastname, isnull(firstname) from nullon
