I want to check if a variable is null. If it is null, then I want to set a value to that variable:
//data type of var is number
if Var = null then
var :=5;
endif
But I am geting error in it. How can I check if a variable is null?
I am using oracle data type
In PL/SQL you can't use operators such as '=' or '<>' to test for NULL
because all comparisons to NULL
return NULL
. To compare something against NULL
you need to use the special operators IS NULL
or IS NOT NULL
which are there for precisely this purpose. Thus, instead of writing
IF var = NULL THEN...
you should write
IF VAR IS NULL THEN...
In the case you've given you also have the option of using the NVL
built-in function. NVL
takes two arguments, the first being a variable and the second being a value (constant or computed). NVL
looks at its first argument and, if it finds that the first argument is NULL
, returns the second argument. If the first argument to NVL
is not NULL
, the first argument is returned. So you could rewrite
IF var IS NULL THEN
var := 5;
END IF;
as
var := NVL(var, 5);
I hope this helps.
And because it's nearly ten years since I wrote this answer, let's celebrate by expanding it just a bit.
The COALESCE
function is the ANSI equivalent of Oracle's NVL
. It differs from NVL
in a couple of IMO good ways:
It takes any number of arguments, and returns the first one which is not NULL. If all the arguments passed to COALESCE
are NULL, it returns NULL.
In contrast to NVL
, COALESCE
only evaluates arguments if it must, while NVL
evaluates both of its arguments and then determines if the first one is NULL, etc. So COALESCE
can be more efficient, because it doesn't spend time evaluating things which won't be used (and which can potentially cause unwanted side effects), but it also means that COALESCE
is not a 100% straightforward drop-in replacement for NVL
.
Always remember to be careful with nulls in pl/sql conditional clauses as null is never greater, smaller, equal or unequal to anything. Best way to avoid them is to use nvl.
For example
declare
i integer;
begin
if i <> 1 then
i:=1;
foobar();
end if;
end;
/
Never goes inside the if clause.
These would work.
if 1<>nvl(i,1) then
if i<> 1 or i is null then
Another way:
var := coalesce (var, 5);
COALESCE is the ANSI equivalent (more or less) of Oracle's NVL function.
There's also the NVL function
use if var is null
Use IS NULL
Source: Stackoverflow.com