An example of an expression used as criteria. This expression will find orders that have not been filled yet, minus three units that are already known to be delayed.
You enter text, a number, or a date in the Criteria cell when you want to find records that have data that is equal to (=) the criteria you enter. Even though you are just entering a simple value, Access formulates an expression behind the scenes for you.
An expression combines values (text or numbers) with built-in functions, fields, calculations, operators (such as greater than >), and constants. Some of its uses are to calculate numbers; set criteria; compare data to a preset value; set a condition (if x is true, then do y); and add text strings together, such as first and last names (sometimes called concatenation).
You can create your own expressions, ranging from a simple comparison (as in sales that are greater than 100,000), to values that fall between two values that you specify, to a calculation (finding delivery dates that are later than three days after the order date).
To create an expression, you can combine text, numbers, dates, identifiers (such as field names), operators (such as = or +), built-in functions , and constants (a preset value that doesn't change, such as True).