Composite keys are table properties that use two columns as the primary keys. A primary key must be a unique value in the table. If there is no available column that is unique in the table, you have the option to create a composite key. A composite key uses the combined values to create a unique value in your table. Primary keys are a part of good table design, and they help with query performance. Composite keys are accomplished in the design view for Microsoft Access.
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Open your Microsoft Access database. Click the "Tables" menu item to list the tables programmed in the database. Right-click the table you want to edit and select "Design View."
Hold the "Ctrl" key on your keyboard. Use the mouse to click both the columns you want to use for the composite key. This highlights both columns simultaneously.
Click the "Primary Key" icon in the main menu. This icon is represented using a key image. Notice the left side of your table columns now display a key, which represents the primary key for a table. Since this is a composite key, both columns have a key.
Click "Save" to save your table changes.