Cover
Introduction
1. How to Retrieve Data From a Single Table
1.1. The Five Clauses of the SELECT Statement
1.2. Column Specifications
1.3. LIKE and REGEXP Operators
1.4. Arithmetic Operators
1.5. Column Aliases
1.6. Comparison Operators
1.7. IS NULL, BETWEEN, IN Operators
1.8. AND, OR, NOT Logical Operators
1.9. DISTINCT Clause
2. How to Retrieve Data from Multiple Tables
2.1. The JOIN Clause
2.2. Joining More Than Two Tables
2.3. The OUTER JOIN Clause
2.4. How to Code a UNION
3. Using Functions
3.1. Date Functions
3.2. Numeric Functions
3.3. String Functions
4. How to Insert, Update, Delete Data in Tables
4.1. The INSERT Clause With a Column List
4.2. The INSERT Clause Without a Column List
4.4. The UPDATE Clause With a Column List
4.4. The DELETE Clause
5. Summary Queries and Aggregate Functions
5.1. Aggregate Functions
5.2. Grouping Data
5.3. Simple GROUP BY Query
5.4. Improving the GROUP BY Query
5.5. Using the HAVING Clause
5.5. Using the HAVING and WHERE Clauses Together
5.6. COUNT(column_name) and COUNT(*)
5.7. Using the DISTINCT Statement
6. Working With Subqueries
6.1. The Subquery In a SELECT Statement
6.2. The Subquery in an UPDATE statement
6.3. Create a Duplicate Table From An Existing Table
6.4. The Subquery In a Delete Statement
7. SQL Views
7.1. SQL View Explained
7.2. Benefits of Using Views
7.3. Views That Allow UPDATE Statements
8. SQL Indexes
8.1. SQL Indexes Explained
8.2. Clustered vs. Non-clustered Indexes
8.3. Create an Index in Workbench Using an ERD
8.4. How to Manually Add an Index to an Existing Table
Glossary
Index
1.5

Column Aliases

Column Aliases

  • A column alias provides a way to create a clean or more descriptive header for a results set.
  • A column alias cannot be used in a SELECT, WHERE, GROUP BY or HAVING clause due to the order of execution. You must refer to the original column name.

In the previous example, we created a new column that was a calculated value. The problem is that the column header is now population / SurfaceArea. However, we can rename the column header to something cleaner by creating a column alias.  Look at the code snippet below.

Example:

SELECT name, population / SurfaceArea
     AS “People per square mile”
FROM country;

We used the AS keyword then in quotes we put the new column alias of “People per square mile.” Which changes the column header as seen show below.

Results:

column_alias.png

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