Difference between revisions of "ISNULL()"
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==Purpose== | ==Purpose== | ||
| − | Function to test if an expression evaluates to NULL | + | Function to test if an expression evaluates to NULL and optionally specify an alternative value for a null expression |
| − | + | ||
==Syntax== | ==Syntax== | ||
| − | ISNULL(< | + | ISNULL(<expr1> [, <expr2>]) |
| − | + | ||
==See Also== | ==See Also== | ||
| − | [[EMPTY()]], [[ISALPHA()]], [[ISBLANK()]], [[ISDIGIT()]], [[NVL()]], [[SET NULL]], [[SET NULLDISPLAY]] | + | [[COALESCE()]], [[EMPTY()]], [[IFNULL()]], [[ISALPHA()]], [[ISBLANK()]], [[ISDIGIT()]], [[NVL()]], [[SET NULL]], [[SET NULLDISPLAY]] |
| − | + | ||
==Description== | ==Description== | ||
| − | The ISNULL() function | + | 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. |
| + | From Lianja v4.2, ISNULL() can also be used to check for the existence of a dynamic array / object member. If the member does not exist, ISNULL() will return .T.; if it does exist, ISNULL() will return .F. | ||
==Example== | ==Example== | ||
<code lang="recital"> | <code lang="recital"> | ||
| − | + | 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 | ||
| + | |||
| + | // Check for existence of dynamic array / object member | ||
| + | declare da[] | ||
| + | da.name = "Lianja Inc" | ||
| + | ? isnull(da["name"]) // .F. | ||
| + | ? isnull(da["address"]) // .T. | ||
</code> | </code> | ||
| − | |||
| − | |||
| − | |||
[[Category:Documentation]] | [[Category:Documentation]] | ||
[[Category:Functions]] | [[Category:Functions]] | ||
| − | [[Category: | + | [[Category:Formatting Functions]] |
| − | + | ||
Latest revision as of 07:17, 13 June 2018
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.
From Lianja v4.2, ISNULL() can also be used to check for the existence of a dynamic array / object member. If the member does not exist, ISNULL() will return .T.; if it does exist, ISNULL() will return .F.
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 // Check for existence of dynamic array / object member declare da[] da.name = "Lianja Inc" ? isnull(da["name"]) // .F. ? isnull(da["address"]) // .T.
