AS

Remarks

Include an AS clause to assign a name to a select term or to a table name. You can use this name elsewhere in the statement to reference the select term. The name is often referred to as an alias.

When you use the AS clause on a nonaggregate column, you can reference the name in WHERE, ORDER BY, GROUP BY, and HAVING clauses. When you use the AS clause on an aggregate column, you can reference the name only in an ORDER BY clause.

The name you define must be unique in the SELECT list.

Column aliases are returned as the column name. Computed columns, including group aggregates, that do not have a column alias specified are assigned a system-generated column name such as EXPR-1, EXPR-2, and so forth.

Examples

The AS clause in the following statement instructs PSQL to assign the name Total to the select term SUM (Amount_Paid) and order the results by the total for each student:

SELECT Student_ID, SUM (Amount_Paid) AS Total

FROM Billing

GROUP BY Student_ID

ORDER BY Total

The keyword AS is optional when used for table aliases as in this next example. When you use the AS clause on a table name in a FROM clause, you can reference the name in a WHERE, ORDER BY, GROUP BY, and HAVING clause.

SELECT DISTINCT c.Name, p.First_Name, c.Faculty_Id

FROM Person AS p, class AS c

WHERE p.Id = c.Faculty_Id

ORDER BY c.Faculty_Id

You can rewrite this query without using the AS clause in the FROM clause as follows.

SELECT DISTINCT c.Name, p.First_Name, c.Faculty_Id

FROM Person p, class c

WHERE p.Id = c.Faculty_Id

ORDER BY c.Faculty_Id

Once you establish a table alias, do not intermix the table name and its alias in a WHERE clause. The following does not work:

SELECT DISTINCT c.Name, p.First_Name, c.Faculty_Id

FROM Person p, class c

WHERE Person.Id = c.Faculty_Id

ORDER BY c.Faculty_Id