Expression Evaluation

[dott]

The expression being evaluated is
if (wdate <> NULL AND wdate < date) then
...
end if


now the error i am getting is "You entered an expression that has no value (2427)

So what i am wondering is is it evaluating the left hand side of the AND expression even though it is seeing that wdate is NULL?

Or is there some other problem here?

 

[Jewellissa]

if (wdate <> NULL AND wdate < date) then
...
end if


AND means both sides have to be true.

If wdate is NULL then it cannot also be a value that is less than date. (Null isn't a value)

Access looks at this and says it is impossible. Any other language would always return False to that logical expression(because they cant both be true) but I guess Access hic-cups.

What you might want is..

if (wdate <> NULL OR wdate < date) then
...
end if

Jewellissa

 

[dott]

Well the point of adding the 'wdate <> null' was so that it wouldnt attempt to evaluate the 'wdate < date' if wdate was null,
so what i wanted to know was does access evaulate a logical AND statement properly or does it evaluate both sides regardless if the first is false anyway

 

[Rich]

If IsDate([SomeField]) Then
If [SomeField] < Date Then

 

[Pat Hartman]

wdate <> NULL does not generate a compile error but it should since it does not work. There is only one way in VBA to test a field for nulls and that is with the IsNull() function. In a query you would use "SomeField Is Not Null" or "SomeField Is Null". I've written a lot here on how nulls work and you can also find good information in help.

if Not IsNull(wdate) AND wdate < date() then

Rich's suggestion also works but obviously only for date fields.