How to use Subqueries In SQL
This method uses a subquery to select the first row from the EmployeeReviews
table for each employee. The subquery is joined to the Employee
table using a LEFT JOIN
to ensure that all employees are included in the result, even if they don’t have a corresponding row in the EmployeeReviews
table..
SELECT
e.EmployeeID,
e.Name,
e.Salary,
firstSalaryReview.ReviewDate,
firstSalaryReview.Rating
FROM
Employee e
LEFT JOIN (
SELECT TOP 1
r.EmployeeID,
r.ReviewDate,
r.Rating
FROM
EmployeeReviews r
ORDER BY
r.ReviewDate
) firstSalaryReview ON e.EmployeeID = firstSalaryReview.EmployeeID;
Output:
Explanation:
- The subquery selects the first row from the
EmployeeReviews
table without any specific ordering. This can lead to unpredictable results because the database engine may return different rows each time the query is executed. - The
LEFT JOIN
ensures that all rows from theEmployee
table are included in the result, even if there is no matching row in the subquery. However, since the subquery doesn’t guarantee a specific row, the result may not always be meaningful.
How to Join to First Row in SQL Server
Joining the first row in SQL Server can be a common requirement in various scenarios, such as when we need to retrieve specific data associated with the first occurrence of a particular group or when you want to fetch additional details related to the first record in a result set.
In this article, We will learn about How to Join to first row in SQL Server by understanding various approaches along with the examples and so on.