SQL分組由價值

Question

的順序出現我有如下表2列

ID  |  Dept 

1  | A  
2  | A 
3  | B 
4  | B 
5  | B 
6  | A 

我想做一個計數使得輸出應該如下表所示。

Dept |  Count 

A  | 2  
B  | 3 
A  | 1 

感謝您的幫助提前！

Answer 1

略有不同，邁克爾的，相同的結果：

with cte1 as (
    select id, 
      dept, 
      row_number() over (partition by dept order by id) - 
      row_number() over (order by id) group_num 
    from  test), 
cte2 as (
    select dept, 
      group_num, 
      count(*) c_star, 
      max(id) max_id 
    from  cte1 
    group by dept, 
      group_num) 
select dept, 
     c_star 
from  cte2 
order by max_id; 

http://sqlfiddle.com/#!4/ff747/1

Answer 2

運行此查詢此：

SELECT Dept, count(*) FROM table_name group By Dept 

Answer 3

你不能用SQL做到這一點。計數會計算不同的項目，因此您的案例中的計數會給您計數A和計數B。

您只能按表格中的值進行計數/分組，而不能按行的順序進行計數/分組。如果您不使用order by，則在SQL中不保證順序。

Answer 4

從你的例子看來，你想要爲每個部門計算連續記錄。

您可以通過組合行號和排序ID來完成此操作。

create table tblDept (
    id int not null, 
    dept varchar(50) 
); 

insert into tblDept values (1, 'A'); 
insert into tblDept values (2, 'A'); 
insert into tblDept values (3, 'B'); 
insert into tblDept values (4, 'B'); 
insert into tblDept values (5, 'B'); 
insert into tblDept values (6, 'A'); 

with orderedDepts as (
    select 
    dept, 
    id, 
    row_number() over (partition by dept order by id) - 
     row_number() over (order by id) as rn 
    from tblDept 
) 
select 
    dept, 
    count(*) as num 
from orderedDepts 
group by 
    dept, 
    rn 
order by 
    max(id) 

給人的輸出：

+------+-----+ 
| DEPT | NUM | 
+------+-----+ 
| A | 2 | 
| B | 3 | 
| A | 1 | 
+------+-----+ 

SQL Fiddle