Selecting Columns

Selecting a Single Column

To retrieve data from a table, you can use the SELECT statement. The SELECT statement specifies the columns to be retrieved from the table.

Syntax

 SELECT column_name
FROM table_name; 

Example

Imagine we have a table called users with the following columns: id , user_name , age , and city .

To retrieve the user_name column from the users table, you can use the following SQL statement:

 SELECT user_name
FROM users; 

This will return the following result:

Exercise 1.1

Run the following code to select the user_name column from the users table.

Exercise 1.2

Write a SQL statement to select the city column from the users table.

Exercise 1.3

Write a SQL statement to select the age column from the users table.

Quiz

Selecting a Column as an Alias

What is an alias? An alias is a temporary name given to a column or a table in a SQL query. You can use aliases to make the output of a query more readable or to shorten the column or table names.

To select a column as an alias, you can use the AS keyword followed by the alias name. For example:

Syntax

 SELECT column_name AS alias_name
FROM table_name; 

Example

To select the user_name column from the users table and give it an alias name , you can use the following SQL statement:

 SELECT user_name AS name
FROM users; 

This will return the following result:

Exercise 1.4

Write a SQL statement to select the user_name column from the users table and give it an alias called name .

Exercise 1.5

Write a SQL statement to select the city column from the users table and give it an alias location .

Selecting Multiple Columns

To select multiple columns we separate the column names with commas.

Sytnax

 SELECT column1, column2
FROM table_name; 

Example

If we need to select age and location from the users table, we would write:

 SELECT age, location
FROM users 

Exercise 1.6

Write a SQL statement to select the city and age columns from the users .

Selecting All Columns

It can be too much effort to type in all columns, and sometimes we may not know what all the columns are. In this case, we can use the * symbol to select all columns.

Syntax

 SELECT *
FROM table_name; 

Example

 SELECT *
FROM users; 

Exercise 1.7

Run the following code to select ALL columns

Exercise 1.8

Write an SQL statement to select ALL columns.

Summary

• To select a single column, use the SELECT statement followed by the column name.

• To select a column as an alias, use the AS keyword followed by the alias name.

• To select multiple columns, separate the column names with commas.

• To select all columns, use the * symbol.

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