Hello guys, if you are wondering how to use the IF EXISTS and NOT EXISTS in SQL then you are at the right place. Earlier, I have shared how to use GROUP BY, WHERE, and HAVING clause and in this tutorial I will share how to use exists and not exists clause in SQL. The IF EXISTS and NOT EXISTS commands in T-SQL are covered in depth in this article. When comparing data sets using subqueries, it also illustrates why EXISTS should be preferred over IN and NOT EXISTS over NOT IN.
If you don't know, EXISTS is a logical operator in SQL that is used to check if rows in a database exist. If the subquery produces one or more records, it returns TRUE.
The NOT EXISTS operator in SQL is the polar opposite of the EXISTS operator, and it is fulfilled if the subquery returns no results.
Using EXISTS in SQL
SELECT column_name FROM Table_Name WHERE EXISTS (SELECT column_name FROM Table_Name WHERE condition);
SELECT * FROM Sales.Customer c WHERE EXISTS (SELECT * FROM Sales.[Order] o WHERE o.CustomerId = o.OrderId)
Using NOT EXISTS in SQL
SELECT column_name FROM Table_Name WHERE NOT EXISTS (SELECT column_name FROM Table_Name WHERE condition);
SQL Exists and Not Exists Example
SELECT * FROM Sales.Customer c WHERE NOT EXISTS IN (SELECT * FROM Sales.[Order] o WHERE o.CustomerId = o.OrderId)
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P.S. - If you are interested in learning Database and SQL and looking for some free resources to start your journey, then you can also take a look at the Introduction to Databases and SQL Querying free course on Udemy to kick-start your learning.
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