When to use SQL Table Alias

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There are two reasons for using table aliases.

The first is cosmetic. The statements are easier to write, and perhaps also easier to read when table aliases are used.

The second is more substantive. If a table appears more than once in the FROM clause, you need table aliases in order to keep them distinct. Self joins are common in cases where a table contains a foreign key that references the primary key of the same table.

Two examples: an employees table that contains a supervisorID column that references the employeeID of the supervisor.

The second is a parts explosion. Often, this is implemented in a separate table with three columns: ComponentPartID, AssemblyPartID, and Quantity. In this case, there won’t be any self joins, but there will often be a three way join between this table and two different references to the table of Parts.

It’s a good habit to get into.

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