LEFT JOIN
JoinReturns all rows from the left table and matching rows from the right table. Unmatched rows get NULL.
Syntax
SELECT cols FROM t1 LEFT JOIN t2 ON condition
Example
SELECT c.name, o.order_id FROM customers c LEFT JOIN orders o ON c.id = o.customer_id;
About SQL LEFT JOIN
The LEFT JOIN keyword belongs to the Join category of SQL statements. Returns all rows from the left table and matching rows from the right table. Unmatched rows get NULL. 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 LEFT JOIN 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 LEFT JOIN: 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.