WHERE Clause in SQL

The WHERE clause in SQL is used to filter records in a query based on specified conditions. It is typically applied in SELECT, UPDATE, DELETE, and other SQL statements to limit the rows affected or returned by the query.

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Key Points

1. Conditional Filtering:
   The WHERE clause filters rows based on one or more conditions, ensuring only relevant data is retrieved or affected.

2. Supports Logical and Comparison Operators:
   You can use operators like =, >, <, LIKE, IN, BETWEEN, and logical operators like AND, OR, and NOT to form complex conditions.

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Syntax

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

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Example

Basic Filtering

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

• Retrieves the first_name and last_name of employees who work in the 'HR' department.

Using Comparison Operators

SELECT first_name, salary
FROM employees
WHERE salary > 50000;

• Returns employees with a salary greater than 50,000.

When to Use the WHERE Clause

• To filter rows in a table based on specific conditions.

• To refine data retrieval for reporting and analytics.

• To apply conditions before performing actions like updating or deleting rows.

Note: If no rows match the condition, the query returns an empty result set.