How Can I Resolve a 'Recursion Depth Limit Exceeded' Error in a Recursive SQL Query?

Solving the "Recursion Depth Limit Exceeded" Error in Recursive Queries

This article addresses a common SQL query error: exceeding the maximum recursion depth. The problem stems from a recursive Common Table Expression (CTE), specifically impacting the EmployeeTree CTE in the example query.

The EmployeeTree CTE recursively retrieves employee data from the tEmployees table, building a hierarchical structure based on matching values in the APV_MGR_EMP_ID and UPS_ACP_EMP_NR columns. However, exceptionally deep hierarchies can trigger the recursion limit (often set to 100), resulting in an error.

The Solution: Enabling Unlimited Recursion

The solution lies in adjusting the query's maxrecursion option. This option controls the maximum recursion depth. Setting it to 0 allows for unlimited recursion, effectively bypassing the error:

...
from EmployeeTree
option (maxrecursion 0)

By adding option (maxrecursion 0), the recursive CTE will continue processing until all matching rows are retrieved, thereby preventing the "recursion depth limit exceeded" error. This approach is suitable when you're confident the recursion will eventually terminate naturally due to the data structure. However, caution is advised; unbounded recursion in poorly designed queries could lead to performance issues or even system instability. Thoroughly test any changes involving infinite recursion.

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