The SQL SELECT statement is used to select (retrieve) data from a database table.
Example
-- select first_name from Customers table
SELECT first_name
FROM Customers;
The above SQL query selects the first_name
of all the customers from the Customers
table.
SQL SELECT Syntax
The syntax of the SQL SELECT
statement is:
SELECT column1, column2, ...
FROM table;
Here,
column1, column2, ...
are the table columnstable
is the table name from where we select the data
For example,
-- select first_name and last_name columns from Customers table
SELECT first_name, last_name
FROM Customers;
Here, the SQL command selects the first_name and last_name of all customers in the Customers
table.
![SQL SELECT Example SQL SELECT first name and last name](/sites/tutorial2program/files/sql-select.png)
SQL SELECT ALL
To select all columns from a database table, we use the *
character. For example,
-- select all columns from Customers table
SELECT *
FROM Customers;
Here, the SQL command selects all columns of the Customers table.
![SQL SELECT All Example SQL SELECT All data from the table](/sites/tutorial2program/files/sql-select-all.png)
SQL SELECT WHERE Clause
A SELECT
statement can have an optional WHERE
clause. The WHERE
clause allows us to fetch records from a database table that matches specified condition(s). For example,
-- select all columns from the customers table with last_name 'Doe'
SELECT *
FROM Customers
WHERE last_name = 'Doe';
Here, the SQL command selects all customers from the Customers table with the last_name Doe.
![SQL SELECT with WHERE example SQL SELECT data WHERE last name is Doe](/sites/tutorial2program/files/sql-where-example.png)
Let's look at another example.
-- select age and country columns from customers table where the country is 'USA'
SELECT age, country
FROM Customers
WHERE country = 'USA';
Here, the SQL command selects the age
and country
columns of all the customers whose country
is USA.
![SQL SELECT with WHERE example SQL SELECT all data WHERE country is USA](/sites/tutorial2program/files/sql-where-example-2.png)
We can also use the WHERE
clause with the UPDATE statement to edit existing rows in a database table.
Note: In SQL, we must enclose textual data inside either single or double quotations like 'USA'
.
SQL Operators
The WHERE
clause uses operators to construct conditions. Some of the commonly used operators are:
1. Equal to Operator (=)
-- select all columns from Customers table with first name 'John'
SELECT *
FROM Customers
WHERE first_name = 'John';
The above SQL command selects all the customers from the Customers table having first_name John.
2. Greater than (>)
-- select all columns from Customers table with age greater than 25
SELECT *
FROM Customers
WHERE age > 25;
The above SQL command selects all the customers from the Customers table whose age is greater than 25.
3. AND Operator (AND)
-- select all columns from Customers table with last_name 'Doe' and country 'USA'
SELECT *
FROM Customers
WHERE last_name = 'Doe' AND country = 'USA';
The above SQL command selects all the customers from the Customers table having last_name Doe and country
USA.
Note: If none of the rows meet the WHERE
clause condition, an empty result set is returned.
To learn more about all the SQL operators in detail, visit SQL Operators.
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