Dealing with null values in ms access

Value or. OldValue is null or nothing -- I'm confused on this point then the inequality fails. I tried updating the part within With ctl to the following. This allows me to log changes for which one of the values before or after was null.

The rest of the commented-out stuff is my attempt to record all of the cases where the value is null, but doesn't change. In other words, the IsNull ctl lets everything through, but I couldn't figure out how to filter the cases of equality back out again.

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Learn more. Ask Question. Asked 9 years, 2 months ago. Active 9 years, 2 months ago. Viewed 4k times. For Each ctl In frm. Controls With ctl 'Avoid labels and other controls with Value property. John John Add a comment. Active Oldest Votes. I also wonder about using it on the Sum instead of on the Amount field. I just ran a quick check and Sum appears to treat Nulls as 0. I'd have to actually benchmark it to see if it made any difference performance-wise.

Pretty much the equivalent in Access is the nz function. Thanks hawbsl! But when i try to execute query using Nz from C code, i get exception that Nz is not defined.

But when using the query from c , i m getting this error message - "Wrong number of arguments used with function in query expression 'IsNull sum amount ,0 '" — IrfanRaza.

Unfortunately if you're accessing the Access database through C then you're using Jet rather than Access itself. Different rules apply and there are various useful functions which aren't available to you. Likewise , can also be used on date and time when sorting Myk Agustin Myk Agustin 7 7 silver badges 27 27 bronze badges. Sign up or log in Sign up using Google.

Sign up using Facebook. Sign up using Email and Password. Occasionally, a null value does mean that the data doesn't exist or isn't valid for that particular record, but the concepts aren't interchangeable. Since Access allows null values, it's your job to determine whether you want to store them. Generally, the data will be your best guide.

If the nature of the data requires that all data be present to save the record, you can handle null values at the table level. Simply set the field's Required property to Yes and bypass the problem. Be prepared for the rules to change. Few applications are so tight that nulls aren't present. If users need the flexibility to create records without entering all of the data at the time they create the record, you have a choice.

Allow the table to store a null value or use a default expression that stores an appropriate text message, such as "NA" or "Pending.

Unfortunately, this solution works only for text fields. For numeric fields, you could use a default value of 0, but that might cause trouble in the long run because functions handle Null and 0 differently see 7. In addition, the Default property works only for new records. That means that you can't apply this solution to existing records. The truth is, it's usually easier to handle null values than it is to usurp them in this fashion.

Don't try to find null values by equating them to anything else. The following expressions return an error, regardless of anything 's value:. As far as Access is concerned, Null doesn't equal anything.

This isn't always true outside Access. Once you decide that null values are acceptable, it's your job to accommodate them throughout the application. For instance, to find null values in a query, you'd enter Is Null in the appropriate field's Criteria cell.

For instance, the use of IsNull in the following If statement handles a potential runtime error when null values exist:. Access won't always work with null values as you might expect. If you allow them, be prepared for surprises. For instance, a simple expression such as.

Instead of returning just the Subtotal, as you might expect, the expression returns Null. That's because any equation that encounters a null value will always return Null.

Although it's a nuisance, it makes sense. You can't evaluate an unknown value. If your data contains null values, use the Nz function to protect your expressions from this error. Specifically, Nz returns a value other than Null when it encounters Null as follows:. In this case, Nz returns 0 when Shipping equals Null.