Renaming Columns - SQL

SQL has no direct counterpart of RENAME. To derive the table on the right in Figure 4.4 from the table on the left, Tutorial D has IS_CALLED RENAME ( StudentId AS Sid ).

                                                    Figure: Tables differing only in a column name

It shows how the same effect can be achieved in SQL. Note that the SELECT clause has to include all the columns that are not subject to renaming, as well as those that are.

Example: Renaming a column

SELECT StudentId AS Sid, Name

FROM IS_CALLED

Explanation

• Each element of a SELECT clause is an expression of arbitrary complexity that can reference one or more columns of the SELECT clause's input table. Note that the expression is not required to reference any columns: it might be just a literal, for example.
• If the expression consists of just a column reference, then the name of the referenced column is the name of the corresponding column in the result.
• If the expression is followed by the key word AS, then the resulting column has the column name given after that key word.

SQL allows the result to have two or more columns of the same name. For example, if we replace Sid by Name in Example, we still have a valid SQL SELECT expression.