Definition of table lookup

step in a manual process or a computer program that involves matching a value (number or word) to another value in a list of paired values and following a prescribed action as dictated by the matched pair. For example, when you look up a telephone number in a directory, you are performing a table lookup. In this case, the person you want to call is the value that you match against a name in the directory. The telephone number is the value paired to the name, and the action is to call that telephone number. The process is the same in a computer environment except that the table is stored electronically rather than on paper.

A table lookup can be used to assign a particular edition of a magazine or catalog to a customer based on his address. For example, in the table that follows, a range of three-digit ZIP code prefixes is paired with various editions of a catalog. The ZIP code in a new customer address is then matched against the prefixes in the table, and the appropriate edition is assigned. For example, a customer living in the 06905 area would be assigned the Northeastern edition.