How do I use a left join in SQL?

How do I use a left join in SQL?

A left join in SQL is used to combine rows from two tables, returning all rows from the left table and matched rows from the right table. If there is no match, NULL values are returned for columns from the right table.

Can you give me an example of a left join?

Sure! Suppose you have two tables: 'Employees' and 'Departments'. You can use a left join to get all employees and their department names like this: SELECT Employees.name, Departments.department_name FROM Employees LEFT JOIN Departments ON Employees.department_id = Departments.id;

What happens if there are no matching records in the right table?

If there are no matching records in the right table, the result will still include the row from the left table, but the columns from the right table will contain NULL values.

Are there any performance considerations when using left joins?

Yes, left joins can be slower than inner joins, especially with large datasets. It's important to ensure that your tables are indexed properly to optimize performance.