When working with SQL, the CASE WHEN statement is a powerful tool that allows you to perform conditional logic within a SELECT query. You can use it to retrieve different values or perform calculations based on specific conditions. In some cases, you might need to include nested SELECT statements within a CASE WHEN clause to achieve more complex logic.

Here is an example of using the CASE WHEN statement with nested SELECT statements in SQL:

SELECT column1, column2,
  CASE 
    WHEN (SELECT COUNT(*) FROM table2) > 0 THEN 'Condition met'
    ELSE 'Condition not met'
  END AS condition_result
FROM table1;

In this example, we have a SELECT query that retrieves values from table1. The CASE WHEN statement is used to check if there are any rows in table2 using a nested SELECT COUNT(*) FROM table2 statement. If the count is greater than 0, the result will be ‘Condition met’. Otherwise, it will be ‘Condition not met’. The AS keyword is used to give the result column a meaningful name (condition_result) in the result set.

Nested SELECT statements can be used to perform more advanced conditions within the CASE WHEN statement. You can include aggregate functions, subqueries, or even joins to retrieve data based on specific criteria.

Remember to replace column1, column2, table1, and table2 with your actual table and column names in your database.

Using nested SELECT statements within a CASE WHEN clause can enhance the flexibility and power of your SQL queries. It allows you to perform complex logic and retrieve conditional data based on specific criteria. Experiment with different scenarios and make sure to optimize your queries for better performance.

#SQL #NestedSelects