Understanding SQL Server with AS Clause

Greetings, Dev! In this article, we are going to explore SQL Server with AS clause. This clause is used to create alias for table and column names. It is a very useful feature which enhances the readability of SQL queries. With the help of AS clause, we can create shorter and more readable queries. Let us dive deeper into this topic and understand it in detail.

What is AS Clause in SQL?

AS is a keyword in SQL which is used to assign an alias to a table or column name. It is used in SELECT, FROM, and JOIN clauses. Let us take a look at an example:

In the above query, we are using AS clause to assign aliases to the emp_name and emp_salary columns. The alias names are EmployeeName and Salary respectively. This query will display the EmployeeName and Salary columns from the employee table.

How AS Clause Works?

The AS clause works by assigning a temporary name to the table or column. This temporary name can be used in the SELECT, FROM, and JOIN clauses. It does not change the actual name of the table or column in the database. Only the temporary name is used in the query result set.

Let us take a look at another example:

In the above query, we are using AS clause to assign a temporary name e to the employee table. We are then using this temporary name in the WHERE clause to filter the results based on the emp_salary column.

Benefits of Using AS Clause

There are several benefits of using AS clause in SQL queries. Some of these benefits are:

• It makes the SQL queries more readable.
• It allows us to use shorter names for tables and columns.
• It helps in avoiding name conflicts between tables and columns.
• It makes it easier to refer to the same table or column multiple times in the same query.

Let us take a look at an example where AS clause can be very useful:

In the above query, we are using AS clause to assign temporary names e1 and e2 to the employee table. We are then using these temporary names in the INNER JOIN clause to join the employee table with itself. We are also using AS clause to assign the ManagerName alias to the emp_name column of the e2 table. This query will display the emp_name, emp_salary and ManagerName columns from the employee table.

FAQs

Q. Can we use AS clause with aggregate functions?

A. Yes, we can use AS clause with aggregate functions. Let us take a look at an example:

In the above query, we are using AS clause to assign the AverageSalary alias to the AVG(emp_salary) aggregate function. This query will display the average salary of all employees in the employee table.

Q. Can we use AS clause with subqueries?

A. Yes, we can use AS clause with subqueries. Let us take a look at an example:

In the above query, we are using AS clause to assign the temporary name t to the subquery. We are then using this temporary name in the WHERE clause to filter the results based on the emp_salary column. This query will display the emp_name and emp_salary columns from the employee table where the emp_salary is greater than the average salary.

Q. Can we use AS clause with table aliases?

A. Yes, we can use AS clause with table aliases. Let us take a look at an example:

In the above query, we are using AS clause to assign temporary names e and m to the employee table. We are then using these temporary names in the INNER JOIN clause to join the employee table with itself. We are also using AS clause to assign the ManagerName alias to the emp_name column of the m table. This query will display the emp_name and ManagerName columns from the employee table.

Conclusion

AS clause is a very useful feature in SQL Server which allows us to create aliases for table and column names. It enhances the readability of SQL queries and makes them more concise. We can use AS clause with SELECT, FROM, and JOIN clauses. It helps in avoiding name conflicts between tables and columns and makes it easier to refer to the same table or column multiple times in the same query. We hope that this article has provided you with a good understanding of AS clause in SQL Server.