Essentials of relating tables

Relating tables simply defines a relationship between two tables. The associated data isn't appended to the layer's attribute table like it is with a join. Instead, you can access the related data when you work with the layer's attributes.

A relate is similar to a simple relationship class except it can involve data from different workspaces (such as a dBASE table can be related to a coverage) and is stored in a layer file or ArcMap document. If you already have a relationship class set up for your data, you can use it as you would a relate in ArcMap.

Relates can be used in the Table and Identify windows to find data that is related to the selected record or records.

The following describes how relates behave when used in ArcMap:

• Relates are bidirectional, therefore both tables involved will be able to use the relate regardless of which table owns the relate. For example, if a relate is created on layerA for tableB, the relate will be listed under layerA, but tableB will be able to use it to access records in layerA.
• When a selection is made on a table or layer, it is not automatically applied to the related tables as it is with links in ArcView GIS 3. You can use the Related Tables command from the Table window's toolbar to apply ("push") a selection to a related table or layer.
• When using the related tables command described above, the related table or layer is added to the table of contents under the active data frame, if necessary, and its Table window is opened.
• If two layers in a map point to the same underlying feature class or shapefile, both are affected by and can use a relate that one of them owns. Since relates can be stored in a specific layer file, one layer can't delete a relate owned by another layer even when both layers refer to the same data.
• A relate owned by a table that is used to define a route or x,y event source layer is not carried over to the event source layer. You must re-create the relate for the event source layer.
• If you relate to a table that does not have an ObjectID column (such as delimited text files or OLE DB tables), you will not be able to apply selections using the relate. The Related Tables command from the Table window's Table Options menu will list the relate, but it will be unavailable. The Identify tool, however, can still be used to find related records.