Mastering Correlated Subqueries in SQL | Step-by-Step Execution Guide | T-SQL Course Part 24 скачать в хорошем качестве

Mastering Correlated Subqueries in SQL | Step-by-Step Execution Guide | T-SQL Course Part 24

What makes a subquery "Correlated"? In this lesson, we break down one of the most powerful yet misunderstood concepts in T-SQL. Unlike standard subqueries, a Correlated Subquery is inter-dependent, executing once for every single row in your main table. What you will learn in this session: Identification: How to spot a Correlated Subquery (Hint: Look for the reference to the outer table inside the inner query!). Step-by-Step Execution: I walk you through the row-by-row "Loop" logic that SQL Server uses to process these queries. The "Outer vs. Inner" Relationship: Understanding how the inner query "waits" for values from the outer query. Practical Use Case: Finding employees whose salary is higher than the average salary of their specific department. - -- THE CHALLENGE: Find employees earning more than their Department's average. -- This is Correlated because the Inner Query needs the 'DepartmentID' -- from the current row of the Outer Query. -- HOW TO IDENTIFY: -- Notice 'OuterEmp.departmentid' inside the subquery? -- That link makes it Correlated! #SQLServer #TSQL #CorrelatedSubquery #SQLProgramming #AdvancedSQL #LearnSQL #DatabaseDevelopment #SQLLogic #DataAnalysis