This tutorial dives deep into Common Table Expressions (CTEs), a powerful SQL feature that defines a temporary, named result set usable within a single query. The core concept of a CTE is introduced through its two main parts: the anchor member, which initiates the result set, and the recursive member, which repeatedly calls the CTE itself, often using the UNION ALL operator. Emphasis is placed on the need for a termination condition in recursive CTEs to prevent infinite loops and errors, noting the default recursion limit of 100. Practical demonstrations show how to construct a simple counting CTE and how to bypass the recursion limit using the OPTION (MAXRECURSION) clause, culminating in a more meaningful example that generates multiplication tables by recursively incrementing values.
The lesson then showcases the real-world application of recursive CTEs by simplifying complex hierarchical data, specifically an employee-manager structure. A sample Employees table with EmployeeID and ManagerID columns is used to represent this tree-view data, which is often difficult to query efficiently. By constructing a recursive CTE, the tutorial illustrates how to trace the complete chain of command for any given employee, all the way up to the CEO. The CTE is designed to iteratively join the employee table to the organization (the CTE itself), increasing a level column with each step of the hierarchy, thereby converting complex organizational relationships into a clear, understandable, and easily traversable structure.
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SQL Queries: https://drive.google.com/file/d/1h8vyl1Ai7_5phF_kXQCZErftyqwZGfjn/view?usp=drive_link