需要每种值类型的行数

Question

我有一个table格式

SID LinkName           
A1  Link1           
A1  Link2           
A2  Link1           
A2  Link2          
A2  Link3         
A3  Link2
A1  Link1
A2  Link2

我需要按以下格式显示每个 link 类型的计数结果

Link1   Link2   Link3                   
 3        4        1

请指教。

编辑：此外，如果我需要以以下格式显示每个 link 类型的不同计数的结果。像A1 -> Link1出现两次但只需要统计一次

Link1   Link2   Link3                   
 2        3        1

Answer 1

select sum(case when LinkName = 'Link1' then 1 end) as link1,
       sum(case when LinkName = 'Link2' then 1 end) as link2,
       sum(case when LinkName = 'Link3' then 1 end) as link3
from tablename

Answer 2

在MySQL中，你可以这样做：

select sum(linkname = 'link1') as link1,
       sum(linkname = 'link2') as link2,
       sum(linkname = 'link3') as link3
from t;

编辑：

如果你想计算不同 sid:

select count(distinct case when linkname = 'link1' then sid end) as link1,
       count(distinct case when linkname = 'link2' then sid end) as link2,
       count(distinct case when linkname = 'link3' then sid end) as link3
from t;

Answer 3

通常你不会把它们放在列中，而是放在行中：

select LinkName, count(LinkName) as LinkCount
from table group by LinkName

...这将给出：

LinkName | LinkCount
Link1    | 2
Link2    | 3
Link3    | 1

那样的话，如果出现新的 link 类型，也没什么大不了的。那行得通吗，还是必须在列中？如果是这样，您可能正在查看单个计数 (*) 和两个子选择或相当复杂的自连接或某种案例方法。喜欢：

select count(*) as Link1, (select count(*) from table where LinkName='Link2') as Link2...
from table where LinkName='Link1'

...或类似的东西。

Answer 4

select Link1,Link2,Link3
from 
(
 select Id,Rtrim(Ltrim(Name)) as Name
 from Table_1
) src
pivot
(
  count(Id)
for Name in (Link1,Link2,Link3)
) piv;

其中给出：

Link1   Link2   Link3
4        3      1

需要每种值类型的行数

Need count of rows for each value type

mysql

sql

group-by

case

where