一個表的不同列中的COUNT值SQL

Question

例如，我的表中有數據--10個志願者。 有兩種類型的志願者 - 學生和工作人員。 如何在一個表中插入數列有這樣的觀點：

COUNT（Volunteer_id），COUNT（Volunteer_id）WHERE Volunteer_type = '學生'， COUNT（Volunteer_id WHERE Volunteer_type = '工作人員'

SELECT COUNT(Volunteer_id) AS "TOTAL VOLUNTEERS" 
from volunteer 
UNION 
SELECT COUNT(Volunteer_id) AS "TOTAL VOLUNTEERS" 
from volunteer 
WHERE Volunteer_type = 'Staff' 
UNION 
SELECT COUNT(Volunteer_id) AS "TOTAL VOLUNTEERS" 
from volunteer 
WHERE Volunteer_type = 'Student' 

該聲明表示爲行現在，但我想讓他們列

Answer 1

使用條件彙總：

SELECT 
    COUNT(*) AS "Total Volunteers", 
    COUNT(CASE WHEN Volunteer_tpye = 'Staff' THEN 1 END) AS "Staff Volunteers", 
    COUNT(CASE WHEN Volunteer_tpye = 'Student' THEN 1 END) AS Student 
FROM volunteers 

Answer 2

DECLARE @volunteer TABLE 
(Volunteer_id int 
,Volunteer_type varchar(50)) 

INSERT INTO @volunteer VALUES (1,'Staff') 
INSERT INTO @volunteer VALUES (1,'Staff') 
INSERT INTO @volunteer VALUES (1,'Staff') 

INSERT INTO @volunteer VALUES (1,'Student') 
INSERT INTO @volunteer VALUES (1,'Student') 
INSERT INTO @volunteer VALUES (1,'Student') 


SELECT COUNT(Volunteer_id) AS "TOTAL VOLUNTEERS" 
     ,(
      SELECT COUNT(tb1.Volunteer_id) AS "TOTAL VOLUNTEERS" 
      FROM @volunteer AS tb1 
      WHERE tb1.Volunteer_id = tb.Volunteer_id 
      AND tb1.Volunteer_type = 'Staff' 


     ) 
     ,(
      SELECT COUNT(volunteer_Student.Volunteer_id) AS "TOTAL VOLUNTEERS" 
      FROM @volunteer AS volunteer_Student 
      WHERE volunteer_Student.Volunteer_id = tb.Volunteer_id 
      AND volunteer_Student.Volunteer_type = 'Student' 
     ) 
FROM @volunteer tb 
GROUP BY tb.Volunteer_id 

Answer 3

試試這個：

select 
    sum(t.x_all) cnt_all, 
    sum(t.x_staff) cnt_staff, 
    sum(t.x_student) cnt_student 
from (
    select 
    1 x_all, 
    case when v.volunteer_type = 'Staff' then 1 else 0 end x_staff, 
    case when v.volunteer_type = 'Student' then 1 else 0 end x_student 
    from volunteer v 
) t