SQL CTE計數孩子的遞歸

Question

我想（使用CTE）以這種方式計算表兒童必須在母公司層面數量，包括他們的孩子所有兒童的。有沒有樣品可用？

Answer 1

CREATE TABLE t_parent (id INT NOT NULL PRIMARY KEY, parentID INT NOT NULL) 

INSERT 
INTO t_parent 
VALUES (1, 0) 
INSERT 
INTO t_parent 
VALUES (2, 1) 
INSERT 
INTO t_parent 
VALUES (3, 1) 
INSERT 
INTO t_parent 
VALUES (4, 2) 
INSERT 
INTO t_parent 
VALUES (5, 1) 
INSERT 
INTO t_parent 
VALUES (6, 5) 
INSERT 
INTO t_parent 
VALUES (7, 5); 

WITH q AS 
     (
     SELECT id, parentId 
     FROM t_parent 
     UNION ALL 
     SELECT p.id, p.parentID 
     FROM q 
     JOIN t_parent p 
     ON  p.id = q.parentID 
     ) 
SELECT id, COUNT(*) 
FROM q 
GROUP BY 
     id