SQL AS Alias
The AS keyword is used to give columns or tables a temporary name that can be used to identify that column or table later. For example,
SELECT first_name AS name
FROM Customers;
Here, the SQL command selects the first_name of Customers. However, its column name will be name instead of first_name in the result set.
SQL AS With More Than One Column
We can also use aliases with more than one column. For example,
SELECT customer_id AS cid, first_name AS name
FROM Customers;
Here, the SQL command selects customer_id as cid and first_name as name.
SQL AS With Expression
We can combine data from multiple columns and represent data in a single column using the CONCAT() function. For example,
SELECT CONCAT(first_name, ' ', last_name) AS full_name
FROM Customers;
Here, the SQL command selects first_name and last_name. And, the name of the column will be full_name in the result set.
More SQL AS Examples
It's a common practice to use AS to create aliases when working with functions. For example,
SELECT COUNT(*) AS total_customers
FROM Customers;
Here, the SQL command counts the total number of rows and represents the value as the total_customers attribute.
The result set of this command will have a total_customers column.
The AS keyword can also be used to give temporary names to tables. For example,
SELECT cu.first_name, cu.last_name
FROM Customers AS cu;
Here, the SQL command temporarily names the Customers table as cu and selects first_name and last_name from cu.
The result set of this command will have first_name and last_name as columns.
We can use AS aliases with table names to make our snippet short and clean while working with JOIN. For example,
SELECT C.customer_id AS cid, C.first_name AS name, O.amount
FROM Customers AS C
JOIN Orders AS O
ON C.customer_id = O.customer_id;
Here, the SQL command temporarily names the Customers table as C and the Orders table as O and selects customer_id from C, first_name from C and amount from O.
The result set of this command will have cid, name and amount columns.
To learn more, visit SQL JOIN.