Alias Syntax
In this lesson, we will learn about assigning aliases to tables and columns.
We'll cover the following
Alias syntax#
You can rename a table or a column temporarily by giving another name known as an Alias. The use of table aliases is to rename a table in a specific SQL statement. Column aliases are used to rename a table’s columns for a particular SQL query. This renaming is a temporary change and the actual table/column name does not change in the database.
Syntax of a table alias#
The basic syntax of a table alias is as follows:
SELECT column1, column2 ... columnN
FROM table_name AS alias_name
WHERE condition;
Example#
For our example, we will be using the following tables:
Customer Table
| ID | NAME | AGE | ADDRESS | SALARY |
|---|---|---|---|---|
| 1 | Mark | 32 | Texas | 50,000 |
| 2 | John | 25 | NY | 65,000 |
| 3 | Emily | 23 | Ohio | 20,000 |
| 4 | Bill | 25 | Chicago | 75,000 |
| 5 | Tom | 27 | Washington | 35,000 |
| 6 | Jane | 22 | Texas | 45,000 |
Orders Table
| ORDER_ID | DATE | CUSTOMER_ID | AMOUNT |
|---|---|---|---|
| 100 | 2019-09-08 | 2 | 5000 |
| 101 | 2019-08-20 | 5 | 3000 |
| 102 | 2019-05-12 | 1 | 1000 |
| 103 | 2019-02-02 | 2 | 2000 |
As you can see in the code above, we temporarily assigned a new alias C to the CUSTOMERS table and O to the ORDERS table.
Furthermore, when working with two tables, we need to specify the table name from which the column is derived, therefore having short aliases helps us to avoid writing large names before each column name. Also, sometimes tables can have the same column names so specifying the table name before the column name helps to avoid confusion regarding which table we are referring to.
In the highlighted lines above, the query simply displays the relevant fields we have selected based on the condition that ID in the CUSTOMERS table is equal to ORDER_ID in ORDERS table. So the result-set is the group of people who have placed orders.
Syntax for a column alias#
The basic syntax of a column alias is as follows:
SELECT column_name AS alias_name
FROM table_name
WHERE condition;
EXAMPLE#
Following is the usage of a column alias.
As you can see in the output above, the column names have changed.
A column alias is particularly useful when we want to change the name of a column to one that is easier to understand for the user.
Quick quiz!#
The following query will change the name of the column ID to CUSTOMER_ID
SELECT ID , NAME AS CUSTOMER_NAME
FROM CUSTOMERS AS CUST
A)
True
B)
False
In the next lesson, we will learn to combine two different tables using joins.
