SQL Select Where ID Not Exist in Another Table

Introduction

When dealing with databases, we often need to extract data from multiple tables. In some cases, we may need to retrieve data from one table that does not exist in another table. In SQL, we can achieve this using the WHERE NOT EXISTS clause.

Syntax

The general syntax for using WHERE NOT EXISTS clause is as follows:

SELECT column_names
FROM table1
WHERE NOT EXISTS (SELECT column_names 
                  FROM table2 
                  WHERE table1.id = table2.id);

In this syntax, we are selecting column_names from table1 where the ID in table1 is not present in table2.

Example

For example, suppose we have two tables, employees and sales. We want to retrieve data for all employees whose sales records are not present in the sales table.

The following SQL query can be used to achieve this:

SELECT *
FROM employees
WHERE NOT EXISTS (SELECT *
                  FROM sales
                  WHERE employees.employee_id = sales.employee_id);

In this query, we are selecting all columns from the employees table where the employee_id is not present in the sales table.

Conclusion

Using the WHERE NOT EXISTS clause can be a powerful tool when working with databases. It allows us to extract data that is not present in another table. This can help us to better understand our data and make more informed decisions.