如果匹配条件，c＃在sql行中计数 [英] c# count in sql row if match condition

问题描述

你好兄弟！我是新的c＃和sql

i现在需要你的帮助^^！



所以，我有一张这样的表



id，parent_id，name

1,0，max

2,1，john

3,1，sean



4,2，truong

5,2，muong

。 .......



（你会看到id 1有2个孩子，id 2有2个孩子）



i想要使代码可以检查sql数据，如果'id'有2'parent_id'将切换到下一个'id'，如果有新的数据插入。 （ps：每个'id'只能容纳2个孩子）

解决方案

所以SQL查询的格式如下：



从[table [join table2 [etc]]中选择[column [，secondcolumn [etc]]



[where子句[和|或] secondclause [etc]]]

[按字段分组[，secondclause [etc]]]

[有子句[和|或secondclause [etc]]]



where子句在平面表上运行，having子句在聚合上运行。



所以，我们可以得到使用一组聚合：

 选择 parent_id，Count（* ） as  '  count' 
 来自  table  
  group   by  parent_id 

Thi列表将如下所示：

parent_id，count

0,1

1,2

2， 2



我们可以在聚合字段'count'上添加一个having子句：

 选择 parent_id，计数（*）为 '  count' 
 来自  table  
  group   by  parent_id 
   count（*）<  2  

现在我们的结果看起来像

parent_id，count

0,1





这就是你需要的吗？

Hi brother! im new in c# and sql
i need your help aout it now ^^!

so, i have a table like this

id, parent_id, name
1, 0, max
2, 1, john
3, 1, sean

4, 2, truong
5, 2, muong
........

(you will see id 1 have 2 child and id 2 have 2 child)

i want to make code can check in sql data if 'id' have 2 'parent_id' will switch to next 'id' if have new data insert. (ps: each 'id' just can hold 2 childs)

解决方案

So the format of an SQL query is as follows:

Select [column [, secondcolumn [etc]]
from [table [join table2 [etc]]
[where clause [and|or secondclause [etc]]]
[group by field [, secondclause [etc]]]
[having clause [ and|or secondclause [etc]]]

where clause operates on the flat table, the having clause operates on aggregates.

So, we can get the aggregate using a group by:

Select parent_id, Count(*) as 'count'
from table
group by parent_id

This list will look like this:
parent_id, count
0, 1
1, 2
2, 2

we can then add a having clause on the aggregate field 'count':

Select parent_id, Count(*) as 'count'
from table
group by parent_id
having count(*) < 2

Now our results look like
parent_id, count
0, 1


Is that what you needed?

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