How Can I Fix 'The maximum recursion 100 has been exhausted' Errors in SQL Recursive CTEs?

Troubleshooting SQL Recursive CTE Errors: Exceeding the Recursion Limit

SQL queries employing recursive Common Table Expressions (CTEs) often hit a "maximum recursion 100 exhausted" error. This arises when the CTE's recursive calls surpass the default recursion limit (usually 100).

Resolving Recursive CTE Errors by Modifying the Query

Let's illustrate with an example retrieving employee data and their hierarchical approval managers:

<code class="language-sql">WITH EmployeeTree AS (
    -- Anchor member of the CTE (initial query)
    ...
    UNION ALL
    SELECT 
        Employees.EMP_SRC_ID_NR, Employees.USR_ACV_DIR_ID_TE, 
        ISNULL(Employees.APV_MGR_EMP_ID, '2')  -- Simplified NULL handling
    FROM 
        dbo.[tEmployees] as Employees WITH (NOLOCK)
    JOIN 
        EmployeeTree ON Employees.APV_MGR_EMP_ID = EmployeeTree.Id 
    WHERE 
        Employees.APV_MGR_EMP_ID IS NOT NULL 
        AND Employees.EMP_SRC_ID_NR IS NOT NULL             
)
SELECT 
    Id AS [EmployeeId], 
    Uuid AS [EmployeeUuid], 
    ApprovalManagerId AS [ManagerId] 
FROM EmployeeTree        </code>

The solution involves the OPTION (MAXRECURSION) clause:

<code class="language-sql">WITH EmployeeTree AS (
    -- Anchor member of the CTE (initial query)
    ...
    UNION ALL
    SELECT ...
    FROM ...
    JOIN EmployeeTree ON ...
)
OPTION (MAXRECURSION 0)
SELECT ...
FROM EmployeeTree        </code>

This clause controls the CTE's recursion depth. Setting MAXRECURSION to 0 disables the recursion limit, effectively preventing the error. However, caution is advised: Infinite recursion can lead to performance issues or crashes if the hierarchical data is improperly structured or contains circular references. Carefully review your data and CTE logic to ensure it terminates correctly before using MAXRECURSION 0. A more robust solution might involve setting MAXRECURSION to a higher, but finite, value, or analyzing the data for potential infinite loops.

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