Are you looking to take your SQL Server skills to the next level? Do you want to stand out in job interviews and impress potential employers with your advanced query writing abilities? Look no further! In this blog post, we will explore some advanced SQL query techniques that will help you excel in your SQL Server career.

One of the common interview questions that separates the junior SQL query writers from the advanced ones is finding the nth highest or lowest value in a table. While most people are familiar with using the TOP keyword to retrieve the top N records, the real challenge lies in finding the record that is in the Nth place based on a specific criteria.

Let’s say we have a table called “Grant” with columns like GrantID, GrantName, EmpID, and Amount. To find the 3rd highest grant amount, we need to rank the records based on the amount and then filter for the record in the 3rd place.

Here’s an example query that sorts the records in descending order based on the amount:

SELECT *
FROM [Grant]
ORDER BY Amount DESC

To rank the records, we can use the RANK() function along with the OVER() clause. The ORDER BY clause is placed inside the OVER() clause to specify the sorting order. The query and its output would look like this:

SELECT *,
RANK() OVER(ORDER BY Amount DESC) AS GrantRank
FROM [Grant]

GrantID | GrantName                 | EmpID | Amount | GrantRank
---------------------------------------------------------------
7       | Ben@MoreTechnology.com    | 10    | 41000  | 1
8       | www.@-Last-U-Can-Help.com | 7     | 25000  | 2
9       | Thank you @.com           | 11    | 21500  | 3

Now, to retrieve only the 3rd highest grant, we can’t directly use the GrantRank alias in the WHERE clause because it is not recognized until after the query has run. To overcome this, we can materialize the query like a table using a Common Table Expression (CTE) or a Derived Table.

Here are examples of using both approaches:

-- Use a Common Table Expression
WITH CTE AS
(
    SELECT *,
    RANK() OVER(ORDER BY Amount DESC) AS GrantRank
    FROM [Grant]
)
SELECT *
FROM CTE
WHERE GrantRank = 3

-- Use a Derived Table
SELECT *
FROM
(
    SELECT *,
    RANK() OVER(ORDER BY Amount DESC) AS GrantRank
    FROM [Grant]
) AS dt
WHERE GrantRank = 3

By materializing the query, we can now filter for the 3rd highest grant and retrieve the desired result.

Mastering advanced SQL query techniques like this will not only help you excel in job interviews but also make you a more efficient and effective SQL Server developer. So, take the time to practice and understand these concepts, and you’ll be well on your way to becoming an SQL expert.

Stay tuned for more SQL Server tips and tricks in our upcoming blog posts!