Access uses the query--1.4. Considerations for performing calculations in a query

4. Considerations for performing calculations in queries

If you want to display the results of a calculation in a field, you can use the predefined calculations or custom calculations that Microsoft Access provides. Using predefined calculations of the so-called "total", you can calculate the following measures for a group of records or for all records: SUM (sum), average (AVG), Quantity (count), Minimum (min), maximum (max), standard deviation (StDev), or variance (Var). You can select the total calculation to be performed on each field.

Aggregate function count cannot include records with null values (NULL) at the time of calculation. For example, the Count function returns the number of all no Null-value records. There is a way to count the null value, or you can convert the null value to zero for calculation. If you want to find the total number of records that contain Null values, use the asterisk (*) wildcard character in Count.

When you display a calculated result in a field, the results are not actually stored in the Datum form. Instead, Microsoft Access will recalculate every time the query is executed so that the results of the calculations always take the most recent data in the database. Therefore, the calculation results cannot be manually updated.