SQL SELECT in Detail | Selecting Specific Columns & Aliases

SELECT

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The SELECT command is the foundation of data retrieval in SQL.

While beginners often start with SELECT *, real world applications require precise and efficient data selection.

In this chapter, we explore:

How to select specific columns

Why selecting only required columns is important

How to use Aliases to rename columns temporarily for better readability

Why Selecting Specific Columns Matters

Using SELECT * retrieves all columns from a table, which may:

Fetch unnecessary data

Reduce query performance

Make results harder to read

Selecting only required columns:

Improves performance

Enhances clarity

Follows professional database practices

Example: employees table

emp_id	emp_name	department	salary
101	Rahul Kumar	Marketing	18,000

Syntax: Selecting Specific Columns

SELECT column1, column2
FROM table_name;

Example

SELECT emp_name, salary
FROM employees;

Result

Only the emp_name and salary columns are displayed.

Selecting Columns in a Preferred Order

The order of columns in the SELECT statement determines the order of output, regardless of the table structure.

SELECT salary, emp_name
FROM employees;

When working with databases, column names are often created for technical clarity, not for presentation.

For example, column names may be:

Too long

Not user-friendly

Written using abbreviations

Difficult to understand in reports

SELECT emp_name, salary * 12
FROM employees;

Although the query works correctly, the output column name for the calculated value may appear unclear or system-generated.

In real-world applications, SQL query results are often:

Shown to end users

Used in reports and dashboards

Exported to Excel or PDF files

In such cases, readable and meaningful column names become important.

An Alias is a temporary name assigned to a column or table only for the result set.

Aliases:

Improve readability

Make column names user-friendly

Are commonly used in reports and dashboards

Syntax

SELECT column_name AS alias_name
FROM table_name;

The keyword AS is optional but recommended for clarity.

Example: Using Column Alias

SELECT emp_name AS Employee_Name, salary AS Monthly_Salary
FROM employees;

Result

The column names in the output appear as:

Employee_Name

Monthly_Salary

Example: Alias Without AS Keyword

SELECT emp_name Employee_Name, salary Monthly_Salary
FROM employees;

This works, but using AS improves readability and is considered a best practice.

Example: Using Aliases with Expressions

Aliases are especially useful when working with calculated values.

SELECT emp_name, salary * 12 AS Annual_Salary
FROM employees;

Important Points to Remember

Aliases do not change the actual column names

They exist only during query execution

Useful for reporting and analysis

Improve query readability

Two Minute Drill

Avoid SELECT* in professional queries
Select only required columns
Column order depends on SELECT clasue
Aliases rename columns temporarily
AS keyword improves clarity
Aliases are comonly used with expressions