WHERE Clause

The SQL WHERE Clause

In SQL, the WHERE clause is used to filter rows returned by a SELECT, UPDATE, or DELETE statement based on specified conditions. It allows you to specify criteria that must be met for a row to be included in the result set or affected by the operation.

Here's the basic syntax of the WHERE clause in a SELECT statement:

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

Explanation of each part:

• SELECT: Keyword indicating that you want to retrieve data from a table.
• column1, column2, ...: The columns you want to retrieve from the table.
• FROM: Keyword indicating the table from which you want to retrieve data.
• table_name: The name of the table from which you want to retrieve data.
• WHERE: Keyword indicating that you want to filter the rows based on specified conditions.
• condition: The condition(s) that must be met for a row to be included in the result set. It can consist of comparisons, logical operators, and functions.

Example:

Suppose we have a table called employees with columns employee_id, first_name, last_name, and department. We want to retrieve the names of employees who work in the Sales department:

SELECT first_name, last_name
FROM employees
WHERE department = 'Sales';

In this example:

• The WHERE clause filters the rows to include only those where the department column equals 'Sales'.
• The result set will contain the first_name and last_name columns of employees who work in the Sales department.

You can also use the WHERE clause in UPDATE and DELETE statements to specify which rows should be updated or deleted based on certain conditions.