SQL脚本 CASE...WHEN...THEN...ELSE...END 的应用

--查找含有A 或 C 站点的车次
drop table SCHEDULETEST;

create table SCHEDULETEST
(
SID     int not null,
CHECI   VARCHAR(8),
CHEZHAN VARCHAR(8)
);

insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (1, 'K1', 'A');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (2, 'K1', 'B');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (3, 'K1', 'C');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (1, 'K1', 'A');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (4, 'K2', 'A');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (5, 'K2', 'B');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (6, 'K2', 'C');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (7, 'K3', 'D');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (8, 'K4', 'D');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (9, 'K5', 'D');
insert into SCHEDULETEST (SID, CHECI, CHEZHAN)
values (9, 'K5', 'C');

select * from scheduletest;

SELECT CHECI as '经过A和C站点的车次'
FROM SCHEDULETEST
WHERE CHEZHAN IN('A','C')
GROUP BY CHECI
HAVING COUNT(distinct SID)>=2;

SELECT CHECI
FROM SCHEDULETEST A
WHERE (CHEZHAN='A' OR CHEZHAN='C')
GROUP BY CHECI
HAVING COUNT(distinct SID)>=2;

--取出每一车次停靠的站点数
select checi '车次',count( distinct chezhan) AS '停靠站点数量'
from SCHEDULETEST
group by checi;

--取出每一车次停靠 A,C的站点次数
select checi AS 车次,
SUM(case chezhan when 'A' THEN 1 ELSE 0 END) '停靠A站点的次数',
SUM(case chezhan when 'C' THEN 1 ELSE 0 END) '停靠C站点的次数'
FROM SCHEDULETEST
GROUP BY CHECI;