SQL SELECT Statement

SQL SELECT Statement

The SELECT statement is the foundation of SQL.
If you want to retrieve, view, filter, or analyse data inside a database table, SELECT is the command you’ll use. Every analytics query, API validation script, or reporting logic starts with a SELECT.

This tutorial covers everything you need to know to get started.

1. What Does the SELECT Statement Do?

SELECT is used to retrieve data from one or more tables.
You can choose:

• Which columns to show
  

• Which rows to show
  

• How the data should be sorted
  

• Whether to remove duplicates
  

• Whether to apply expressions or calculations
  

Basic syntax:

SELECT column1, column2, ...

FROM table_name;

2. Selecting All Columns

If you want to fetch all the columns from a table, use the asterisk (*):

SELECT *

FROM Employees;

This returns every row and every column in the Employees table.

⚠️ Tip for professionals:
Avoid using SELECT * in production queries. It slows performance and returns unwanted columns. Use only the columns you actually need.

3. Selecting Specific Columns

Instead of selecting all columns, you can list only the columns you need:

SELECT FirstName, LastName, City

FROM Employees;

This makes the output cleaner and the query faster.

4. Using Column Aliases (AS)

-- Aliases let you rename output columns, making results more readable:

SELECT 

    FirstName AS "First Name",

    Salary AS "Monthly Salary"

FROM Employees;

-- You can also skip the AS keyword:

SELECT FirstName "First Name"

FROM Employees;

Aliases are extremely useful in reporting, joins, and calculations.

5. Selecting Distinct Values (DISTINCT)

If a column contains repeated values, DISTINCT removes duplicates.

-- Example: Get unique job titles:

SELECT DISTINCT JobTitle

FROM Employees;

-- Example: Unique combinations of department and city:

SELECT DISTINCT Department, City

FROM Employees;

6. Sorting Data with ORDER BY

-- The default order is ascending (ASC). Use DESC for descending.

SELECT FirstName, LastName, Salary

FROM Employees

ORDER BY Salary DESC;

-- You can sort by multiple columns:

SELECT FirstName, LastName, City, Salary

FROM Employees

ORDER BY City ASC, Salary DESC;

7. Limiting the Number of Rows

Different databases use different keywords:

-- MySQL / PostgreSQL:

SELECT *

FROM Employees

LIMIT 5;

-- SQL Server:

SELECT TOP 5 *

FROM Employees;

-- Standard SQL:

SELECT *

FROM Employees

FETCH FIRST 5 ROWS ONLY;

8. Using Expressions in SELECT

-- You can return calculated columns:

SELECT 

    FirstName,

    LastName,

    Salary,

    Salary * 12 AS AnnualSalary

FROM Employees;

-- Example: Concatenate columns:

SELECT

    FirstName || ' ' || LastName AS FullName

FROM Employees;

(Some databases use CONCAT() instead.)

9. SELECT with WHERE (Preview)

-- You can apply conditions to filter rows:

SELECT *

FROM Employees

WHERE City = 'London';

You will learn all filtering conditions in the next topic (SQL WHERE).

10. A Complete Practical Example

Imagine a table:

Projects

-- Let’s write a useful business query:

SELECT 

    ProjectName AS "Project",

    Budget,

    Budget * 1.2 AS "Revised Budget",

    Status

FROM Projects

WHERE Status = 'Active'

ORDER BY Budget DESC;

Result:

This shows how SELECT can combine:

• Filtering
  
• Sorting
  
• Aliasing
  
• Expressions
  

11. Summary Checklist

By now, you should be able to:

✔ Use SELECT to retrieve data

✔ Fetch all or specific columns

✔ Rename columns with aliases

✔ Remove duplicates with DISTINCT

✔ Sort results using ORDER BY

✔ Limit rows depending on DB system

✔ Use basic expressions inside SELECT