Column aliases with AS in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a column alias in SQL?

A column alias is a temporary name given to a column in the result set of a query to make the output easier to read or understand.

beginner

How do you use the AS keyword in SQL?

You use AS to assign a new name (alias) to a column or expression in the SELECT statement, like: SELECT column_name AS alias_name FROM table_name;

beginner

Why would you use a column alias in a query?

To make column names more readable, to rename complex expressions, or to prepare output for reports or user interfaces.

intermediate

Can you use column aliases without the AS keyword?

Yes, in many SQL dialects you can write SELECT column_name alias_name FROM table_name; but using AS improves clarity.

beginner

Example: Write a query to select the column 'price' from 'products' table and rename it to 'Cost'.

SELECT price AS Cost FROM products;

What does the AS keyword do in SQL?

A Deletes a column from a table

B Creates a new table

C Assigns a temporary name to a column or expression

D Filters rows in a query

AS is used to give a temporary name (alias) to a column or expression in the query result.

Which of the following is a correct way to alias a column named 'salary' as 'Income'?

A SELECT salary AS Income FROM employees;

B SELECT salary Income FROM employees;

C SELECT salary = Income FROM employees;

D SELECT salary INTO Income FROM employees;

The correct syntax uses AS to assign the alias: SELECT salary AS Income FROM employees;

Is the AS keyword mandatory when creating a column alias?

A Only mandatory in SELECT * queries

B Yes, always mandatory

C Only mandatory for table aliases

D No, it is optional in many SQL dialects

AS is optional in many SQL dialects but recommended for clarity.

What will this query return? SELECT price AS Cost FROM products;

A A column named 'Cost' with data from 'price'

B All columns from products table

C An error because AS is not allowed

D A column named 'price' with original data

The query returns the 'price' column data but names the column 'Cost' in the output.

Why might you want to use a column alias?

A To change the data type of a column

B To make output easier to read or understand

C To permanently rename a column in the table

D To delete a column from the table

Column aliases help make query results clearer without changing the actual table.

Explain what a column alias is and how to use the AS keyword in SQL.

Think about how you rename columns temporarily in query results.

Describe why column aliases are useful when writing SQL queries.

Consider how output looks to users or reports.