How to use SQL alias in an expression without selecting it?

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You can use SQL aliases in an expression without selecting it by using the keyword "AS" followed by the alias name in the expression.

For example, if you have a table "Customers" with columns "FirstName" and "LastName" and you want to combine those columns into a new column "FullName" without selecting the individual columns, you could use the following SQL statement:

SELECT CONCAT(FirstName, ' ', LastName) AS FullName FROM Customers;

In this example, the "AS FullName" part of the expression creates an alias for the CONCAT function, so the result of the expression is a column named "FullName" with the concatenated values of the FirstName and LastName columns.