A lookup is a FileMaker relationship related term and will copy the information from a child table occurrence into a field in the parent table occurrence. The copying of information is triggered when the parent match field in a relationship had data first entered into it or data is refreshed.
To define a lookup field, highlight the field in the FileMaker Manage Fields Dialog Box that you want to perform lookups and click the options button. From here you will want to click the Auto-Enter Tab, if it wasn’t the default view when you opened that dialog box (quite often it is).
Next you will want to click the option to define the auto enter to take place via a lookup operation. The auto enter via lookup area has a check box to the left and a button on the right. When you don't have a lookup specified, you can click either the box or the Specify button to bring up the pick relationship dialog box.
NOW HERE IT CAN BECOME A LITTLE TRICKY FOR THE FILEMAKER 6 PERSON WORKING WITH NEWER VERSIONS OF FILEMAKER! - You will see two pull down menus ( Starting with table ) and ( Lookup from related table ). By default, the table you start with will be the table used for the layout you currently are on. However, you must remember that FileMaker 7 can have multiple tables and multiple table occurrences. This becomes clear when you try to set the "Lookup from table " menu. It will show you the available related tables based upon the first menu setting ( Starting With Table ). The selection you make from the ( Lookup from related table ) field will bring up a list of fields in that table that can be used for the lookup process. Select the field you want to copy information from, when the lookup is executed.
A lookup can take place in at least five different situations. When data is first entered into a parent field of a relationship, the lookup is executed for that record. When data is edited in a parent field of a relationship, the lookup is executed for that record. When the replace command is executed within a parent key field of a relationship, the lookup is executed for all the records in the found set. When data is imported in from another file into a parent field of a relationship, the lookup is executed for that record ( note ... this can be turned off via one of the import dialog boxes). There is also a relookup command under the File menu and as a ScriptMaker step. When the relookup command is executed for a parent key field of a relationship, the lookup is executed for that record.
FYI... Lookups can be calculated! Now there are two functions in the logical function family that work with lookup operations. They are Lookup and LookupNext ( check them out ! ).