What are SQL join and aggregate functions?

Can you explain what SQL join and aggregate functions are?

Sure! SQL join functions are used to combine rows from two or more tables based on a related column. Aggregate functions, on the other hand, perform calculations on a set of values and return a single value, like SUM, AVG, or COUNT.

How do I use a JOIN with an aggregate function in a query?

You can use a JOIN in combination with an aggregate function by first joining the tables and then applying the aggregate function in the SELECT statement. For example: SELECT department, COUNT(*) FROM employees JOIN departments ON employees.department_id = departments.id GROUP BY department;

What types of JOINs are there in SQL?

There are several types of JOINs in SQL, including INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN. Each serves a different purpose in how data is combined.

Can you give me an example of a query using a LEFT JOIN and an aggregate function?

Certainly! Here's an example: SELECT d.name, COUNT(e.id) AS employee_count FROM departments d LEFT JOIN employees e ON d.id = e.department_id GROUP BY d.name; This will give you the count of employees in each department, including departments with no employees.