根据HEAD（父） - sql隔离行

Question

我有以下SQL表。

+----+--------+----------+--------+
| ID | TestNo | TestName | HeadID |  
+----+--------+----------+--------+
|  1 |     21 | Comp-1   |  null  |   
|  2 |     22 | C1       |  21    |   
|  3 |     23 | C2       |  21    |   
|  4 |     24 | C3       |  21    |   
|  5 |     47 | Comp-2   |  null  |   
|  6 |     25 | C4       |  47    |   
|  7 |     26 | C1+      |  21    |   
+----+--------+----------+--------+

我希望在他们的头部测试下得到所有子行（根据他们的HeadID）。

select * from ranges order by HeadID

ACTUAL OUPUT 我从以上查询得到：

+----+--------+----------+--------+
| ID | TestNo | TestName | HeadID |  
+----+--------+----------+--------+
|  1 |     21 | Comp-1   |  null  |   
|  5 |     47 | Comp-2   |  null  |   
|  2 |     22 | C1       |  21    |   
|  3 |     23 | C2       |  21    |   
|  4 |     24 | C3       |  21    |   
|  7 |     26 | C1+      |  21    |   
|  6 |     25 | C4       |  47    |   
+----+--------+----------+--------+

但我的渴望的输出是：

+----+--------+----------+--------+
| ID | TestNo | TestName | HeadID |   
+----+--------+----------+--------+
|  1 |     21 | Comp-1   |  null  |   
|  2 |     22 | C1       |  21    |   
|  3 |     23 | C2       |  21    |  
|  4 |     24 | C3       |  21    |   
|  7 |     26 | C1+      |  21    |   
|  5 |     47 | Comp-2   |  null  |  
|  6 |     25 | C4       |  47    |   
+----+--------+----------+--------+

我怎样才能做到这一点？

Answer 1

如果你只有一个级别的孩子，那么你可以这样订购：

SELECT *
FROM Ranges
ORDER BY
    CASE WHEN HeadID IS NULL THEN TestNo ELSE HeadID END
    ,HeadID
    ,ID
;