SELECT all columns in SQL

Introduction

We use SELECT all columns to get every piece of information from a table without listing each column name.

You want to see all details about customers in a customer table.

You need to check all data in a product list quickly.

You are exploring a new table and want to understand what data it holds.

You want to export all information from a table to another system.

You want to debug or verify all columns in a table.

Syntax

SQL

SELECT * FROM table_name;

The asterisk (*) means 'all columns'.

Replace table_name with the actual name of your table.

Examples

This gets all columns and rows from the employees table.

SQL

SELECT * FROM employees;

This gets all columns but only for orders made on January 1, 2024.

SQL

SELECT * FROM orders WHERE order_date = '2024-01-01';

This gets all columns but only the first 5 rows from the products table.

SQL

SELECT * FROM products LIMIT 5;

Sample Program

This creates a simple table called fruits, adds three rows, then selects all columns and rows.

SQL

CREATE TABLE fruits (id INT, name VARCHAR(20), color VARCHAR(20));
INSERT INTO fruits VALUES (1, 'Apple', 'Red'), (2, 'Banana', 'Yellow'), (3, 'Grape', 'Purple');
SELECT * FROM fruits;

Important Notes

Using SELECT * is easy but can be inefficient if the table has many columns and you only need a few.

Always consider listing columns explicitly in large or production queries for better performance and clarity.

Summary

SELECT * fetches all columns from a table.

It is useful for quick checks or when you need every piece of data.

Use it carefully in big tables to avoid slow queries.

Practice

1. What does the SQL query SELECT * FROM employees; do?

easy

A. It deletes all data from the employees table.

B. It creates a new employees table.

C. It updates all columns in the employees table.

D. It retrieves all columns and all rows from the employees table.

Solution

1. Step 1: Understand the SELECT * syntax

   The asterisk (*) means select all columns from the specified table.

2. Step 2: Apply to the employees table

   The query fetches every column and every row from the employees table.

3. Final Answer:

   It retrieves all columns and all rows from the employees table. -> Option D

4. Quick Check:

   SELECT * = all columns and rows [OK]

Hint: SELECT * means get everything from the table [OK]

Common Mistakes:

• Thinking SELECT * deletes or updates data
• Confusing SELECT * with creating tables
• Assuming it selects only one column

2. Which of the following is the correct syntax to select all columns from a table named products?

easy

A. SELECT * FROM products;

B. SELECT products.*;

C. SELECT columns FROM products;

D. SELECT ALL FROM products;

Solution

1. Step 1: Recall the correct SELECT syntax

   The correct way to select all columns is using SELECT * FROM table_name.

2. Step 2: Check each option

   SELECT * FROM products; matches the correct syntax exactly.

3. Final Answer:

   SELECT * FROM products; -> Option A

4. Quick Check:

   SELECT * FROM table = correct syntax [OK]

Hint: Use SELECT * FROM table_name to get all columns [OK]

Common Mistakes:

• Using SELECT ALL instead of SELECT *
• Forgetting FROM keyword
• Trying to select 'columns' literally

3. Given the table students with columns id, name, and age, what will the query SELECT * FROM students WHERE age > 20; return?

medium

A. All students regardless of age.

B. Only the age column for students older than 20.

C. All columns for students whose age is greater than 20.

D. An error because * cannot be used with WHERE.

Solution

1. Step 1: Understand SELECT * with WHERE clause

   SELECT * fetches all columns, and WHERE filters rows based on condition.

2. Step 2: Apply condition age > 20

   Only rows where age is greater than 20 are returned, with all columns shown.

3. Final Answer:

   All columns for students whose age is greater than 20. -> Option C

4. Quick Check:

   SELECT * + WHERE filters rows [OK]

Hint: SELECT * returns all columns; WHERE filters rows [OK]

Common Mistakes:

• Thinking WHERE limits columns instead of rows
• Assuming * selects only one column
• Believing * cannot be used with WHERE

4. Identify the error in this SQL query: SELECT * employees;

medium

A. Table name should be in quotes.

B. Missing FROM keyword before table name.

C. Using * is not allowed in SELECT.

D. SELECT cannot be used without WHERE.

Solution

1. Step 1: Check SQL SELECT syntax

   The correct syntax requires FROM before the table name.

2. Step 2: Identify missing keyword

   The query misses FROM between SELECT * and employees.

3. Final Answer:

   Missing FROM keyword before table name. -> Option B

4. Quick Check:

   SELECT * FROM table is correct syntax [OK]

Hint: Always use FROM before table name in SELECT [OK]

Common Mistakes:

• Omitting FROM keyword
• Thinking * is invalid
• Adding unnecessary quotes around table name

5. You want to quickly check all data in a large table named orders. Which query is best to avoid slowing down your database?

hard

A. SELECT * FROM orders LIMIT 10;

B. SELECT * FROM orders;

C. SELECT order_id FROM orders;

D. DELETE FROM orders WHERE order_id < 10;

Solution

1. Step 1: Understand SELECT * impact on large tables

   SELECT * fetches all rows and columns, which can be slow on big tables.

2. Step 2: Use LIMIT to reduce rows fetched

   Adding LIMIT 10 fetches only 10 rows, making the query faster and safer.

3. Final Answer:

   SELECT * FROM orders LIMIT 10; -> Option A

4. Quick Check:

   LIMIT reduces rows, speeding up SELECT * [OK]

Hint: Use LIMIT with SELECT * on big tables to speed queries [OK]

Common Mistakes:

• Running SELECT * without LIMIT on large tables
• Confusing DELETE with SELECT
• Selecting only one column when all data is needed