What is the VB code for looking up a value in a table?

[mseo]

While that's true Chris, it's one of those things that should rarely, if ever, cause a problem.

If it's used in such a way to cause any sort of noticeable delay, then the code design is almost certainly poor. Generally it's run after an operator has intervened in some way, and compared to operator times the fraction of a second of difference that it makes is hard to notice. If it's used in such a way as to be called a number of times within such a window then the performance degradation may be noticeable. In such a situation though, I'd focus my attention on the code design rather than the Domain Aggregate functions.

hi,
thanks for your comment
this code, I have used it many times and it works fine, without any delay

[mseo]

ok, Neopa,I am completely agree with you and munkee
I am wrong
I need to know, what's the difference between Null and Zero-lenght string?

[munkee]

null has no value whereas zero length has been assigned a "blank" value

[mseo]

I've never seen any evidence of that MSEO. In what way have you found there to be a problem? Is this a case of not handling the returned result correctly perhaps?

so why would I use something like this with datatype number fields:

Nz(DLookup("[fieldname in the table]", _ 
           "table name", _ 
           "[fieldname in the table] = " & Me.textbox control name& ""))

[NeoPa]

mseo: I need to know, what's the difference between Null and Zero-lenght string?

Null is not a value as such at all. It is an indicator of an absence of a value.

An empty string, on the other hand, is a string value that simply has no characters in it. Strings can be of any length from 0 characters upwards, to the upper limit. Of the VBA variable types (excluding any object types), only Variant can possibly hold a Null, as standard variables are designed to hold values of a specific type only and Null is none of those.

I hope this clarifies things for you somewhat :)

[NeoPa]

mseo: so why would I use something like this with datatype number fields:

Nz(DLookup("[fieldname in the table]", _ 
           "table name", _ 
           "[fieldname in the table] = " & Me.textbox control name& ""))

Good question. That's code that cannot possibly compile.

If you are asking why the use of Nz() for a number field then that's a different story.

First of all, the Nz() is applied to the DLookup() call and not the field. If you check the Help system for DLookup() you'll see it returns a Null if nothing is found.

Secondly, fields are not VBA variables. They are designed to have the possibility of containing Nulls. This is configurable in the design of your table fields, but the possibility is there.

[NeoPa]

A new, and unrelated question was asked in this thread by the OP which has now been moved to Clear Error Message from TextBox. This is against our rules and I'd ask that you create new threads for your questions please.