Bits of .NET

Nested subqueries are impossible to read. CTEs (Common Table Expressions) break them into named, readable chunks.

Messy Nested Query:

SELECT *
FROM Orders o
WHERE o.CustomerId IN (
    SELECT CustomerId
    FROM Customers
    WHERE Country IN (
        SELECT Country
        FROM TopCountries
        WHERE Revenue > 1000000
    )
);

Clean CTE Version:

WITH TopCountries AS (
    SELECT Country
    FROM CountryRevenue
    WHERE Revenue > 1000000
),
TopCustomers AS (
    SELECT CustomerId
    FROM Customers
    WHERE Country IN (SELECT Country FROM TopCountries)
)
SELECT *
FROM Orders
WHERE CustomerId IN (SELECT CustomerId FROM TopCustomers);

-- Much more readable!

Multiple CTEs:

WITH 
    SalesData AS (SELECT ...),
    RevenueData AS (SELECT ...),
    CombinedData AS (SELECT ... FROM SalesData JOIN RevenueData)
SELECT * FROM CombinedData;

Like defining functions – reusable and clear!