使用SQL Server另一列中的行值计数更新列

Question

我不知道为什么我还没有找到一个解决这个放在这里，但是：我想COUNT了多少次Serial_Parent在包装阶段出现这样我就可以在其他计算中使用。

这完美地工作：

SELECT 
    Serial_Parent, COUNT(Serial_Parent)
FROM 
    mfng_data
WHERE 
    Machine_Process = 'Packing'
GROUP BY 
    Serial_Parent;

但是，当我尝试使用此COUNT来UPDATE列时，我却惨败，因为它只对表中的所有行进行计数并将其保存为每个行值，因此在每个行值中出现2,134,222。

我已经试过了：

UPDATE mfng_data
SET Count_Serial_Parent = (SELECT COUNT(*)
                           FROM mfng_data 
                           WHERE Machine_Process = 'Packing'
                             AND Serial_Parent = Serial_Parent) 
WHERE Serial_Parent = Serial_Parent;

我也尝试过这个：

UPDATE mfng_data
SET Count_Serial_Parent = (SELECT COUNT(Serial_Parent)
                           FROM mfng_data 
                           WHERE Machine_Process = 'Packing'
                             AND Serial_Parent = Serial_Parent);

样本数据：

Spec: 12373  Rev: -6    M35846  M358461 M3584610    M35846101   NULL    NULL    NULL    M35846101   6808
Spec: 12373  Rev: -6    M35846  M358461 M3584610    M35846102   NULL    NULL    NULL    M35846102   6808
Spec: 16692  Rev: -4    K45678  K456781 K4567810    K45678101   NULL    NULL    NULL    K45678101   3964
Spec: 16692  Rev: -4    K45678  K456782 K4567820    K45678201   NULL    NULL    NULL    K45678201   3978
Spec: 16693  Rev: -4    K45678  K456782 K4567820    K45678202   NULL    NULL    NULL    K45678202   3806

所需的结果（M35846将出现两次，因此每行条目将列出“ 2”）

Serial_Parent Count_Serial_Parent
----------------------------------
M35846           2
M35846           2
J39384          52 - - > 52 rows will show "52" and so on below
M35488          10
K4448            4
M35927           8
K45678           3

Answer 1

您需要表别名和合格的列名：

UPDATE m
    SET Count_Serial_Parent = (SELECT COUNT(*)
                               FROM mfng_data m2
                               WHERE m2.Machine_Process = 'Packing' AND
                                     m2.Serial_Parent = m.Serial_Parent 
                              )
    FROM mfng_data m;

子查询需要与外部查询相关 。 诸如Serial_Parent = Serial_Parent类的条件基本上总是评估为true，因为它引用的是子查询中引用的表的列。

但是，更好的方法是更新CTE：

with toupdate as (
      select m.*,
             sum(case when m.Machine_Process = 'Packing' then 1 else 0 end) over (partition by m.serial_parent) as new_Count_Serial_Parent 
      from  mfng_data m
     )
update toupdate
    set Count_Serial_Parent = new_Count_Serial_Parent;

Answer 2

另一种方法（使用玩具桌-希望您能想到这个主意）：

DECLARE @ TABLE (Serial_Parent int, Count_Serial_Parent int)
INSERT INTO @ (Serial_Parent, Count_Serial_Parent) VALUES
(1,0), (1,0),(2,0),(2,0),(2,0)
SELECT * FROM @

UPDATE m -- mfng_data

SET m.Count_Serial_Parent = j.Count_Serial_Parent
FROM @ m -- mfng_data
JOIN (
SELECT Serial_Parent, COUNT(*) Count_Serial_Parent
FROM @ 
GROUP BY Serial_Parent
) j ON j.Serial_Parent = m.Serial_Parent

SELECT * FROM @