WHEN

Conditional

Specifies a condition within a CASE expression.

Syntax

CASE WHEN condition THEN result

Example

SELECT status,
  CASE status
    WHEN 'active' THEN 'Active'
    WHEN 'inactive' THEN 'Inactive'
    ELSE 'Unknown'
  END AS label
FROM accounts;

About SQL WHEN

The WHEN keyword belongs to the Conditional category of SQL statements. Specifies a condition within a CASE expression. Understanding this command is essential for any developer working with relational databases like PostgreSQL, MySQL, SQLite, or SQL Server.

SQL (Structured Query Language) is the standard language for managing and querying relational databases. The WHEN statement is supported across all major database systems, though specific syntax may vary slightly between PostgreSQL, MySQL, MariaDB, Oracle, SQL Server, and SQLite. Always consult your database's documentation for vendor-specific features and limitations.

Best practices for using WHEN: always test queries on a development database before running them in production, use parameterized queries to prevent SQL injection, and leverage EXPLAIN to understand query performance. For complex queries, consider using CTEs (Common Table Expressions) to improve readability and maintainability.

Related SQL Keywords

CASECOALESCE