SQL WHERE Clause

The WHERE clause in SQL is used to filter records from a table based on specified conditions. It allows you to select only the rows that meet certain criteria, making your queries more precise and efficient.

WHERE Clause: Definition and Usage

The WHERE clause comes after the FROM clause in a SELECT statement (and can be used with other SQL statements like UPDATE and DELETE). It lets you specify conditions that must be met for a row to be included in the result set. This dramatically reduces the amount of data returned, making queries faster and easier to manage.

Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition;
      

Example Database: Customers Table

Let's use this sample 'Customers' table for the following examples:

Examples Using WHERE

Selecting Customers from a Specific Country

This query retrieves all customers from Mexico.

SELECT * FROM Customers
WHERE Country = 'Mexico';
      

(Only Customers where Country is 'Mexico' will be returned)
      

Data Types and Quotes

Remember to enclose text values in single quotes, but not numeric values.

SELECT * FROM Customers
WHERE CustomerID = 1;
      

(Only the customer with CustomerID 1 will be returned)
      

Using Comparison Operators

This query retrieves customers with a CustomerID greater than 80.

SELECT * FROM Customers
WHERE CustomerID > 80;
      

(Customers with CustomerID greater than 80 will be returned)
      

Available Operators in WHERE Clause