使用mysql管理器下的員工遞歸計數

Question

我需要下列表格中管理員使用MYSQL的層次結構後所有員工的列表。在oracle或mssql中很容易，但在MySQL中找不到任何解決方案。任何人都可以幫我解決這個問題。

id name manager 

1 John 6 
2 Gill 7 
3 Ben  2 
4 Roy  8 
5 Lenin 6 
6 Nancy 7 
7 Sam  0 
8 Dolly 3 

Answer 1

如果你仍然可以限制最大級別的數量，這是一個遞歸過程的解決方案。由於遞歸函數在MySQL中是不允許的，我們在這裏有一個函數（manager_count），它包含了遞歸過程的結果。遞歸深度由max_sp_recursion_depth變量控制，該變量爲takes 255 as its maximum。使用方法如下：SELECT *,manager_count(id) FROM my_table。這不是最佳的解決方案，因爲它沒有考慮到層次結構的已計數分支（臨時表實際上可以用作緩存）。

DELIMITER // 
DROP FUNCTION IF EXISTS manager_count// 
CREATE FUNCTION manager_count(_manager INT) RETURNS INT 
BEGIN 
    DECLARE _count INT DEFAULT 0; 
    SET max_sp_recursion_depth = 255; 
    # manager_count_helper does the job 
    CALL manager_count_helper(_manager, _count); 
    # subtract 1, because manager_count_helper will count this manager as well 
    RETURN _count - 1; 
END// 

DROP PROCEDURE IF EXISTS manager_count_helper// 
CREATE PROCEDURE manager_count_helper(IN _manager INT, INOUT _count INT) 
BEGIN 
    IF EXISTS (SELECT 1 FROM my_table WHERE id = _manager) THEN 
    BEGIN 
     DECLARE _next_manager INT DEFAULT 0; 
     DECLARE done BOOLEAN DEFAULT FALSE; 
     # cursor to loop through the employees 
     DECLARE _cursor CURSOR FOR SELECT id FROM my_table WHERE manager = _manager; 
     # if done, the done variable gets TRUE and it's time too leave 
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; 
     # count 1, because this guy should be counted as well 
     SET _count = _count + 1; 
     OPEN _cursor; 
     read_loop: LOOP 
      FETCH _cursor INTO _next_manager; 
      IF done THEN LEAVE read_loop; 
      END IF; 
      CALL manager_count_helper(_next_manager, _count); 
     END LOOP; 
     CLOSE _cursor; 
    END; 
    END IF; 
END