表的創建
CREATE TABLE `lee` ( `id` int(10) NOT NULL AUTO_INCREMENT, `name` char(20) DEFAULT NULL, `birthday` datetime DEFAULT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8
數據插入:
insert into lee(name,birthday) values ('sam','1990-01-01'); insert into lee(name,birthday) values ('lee','1980-01-01'); insert into lee(name,birthday) values ('john','1985-01-01');
第一種用法:
SELECT name, CASE WHEN birthday < '1981' THEN 'old' WHEN birthday > '1988' THEN 'yong' ELSE 'ok' END YORN FROM lee
第二種用法:
SELECT NAME, CASE name WHEN 'sam' THEN 'yong' WHEN 'lee' THEN 'handsome' ELSE 'good' END as oldname FROM lee
第三種:當然了,case when 語句還可以復合
select name, birthday, case when birthday > '1983' then 'yong' when name='lee' then 'handsome' else 'just so so' end from lee;
在這裡用sql語句進行日期比較的話,需要對年加引號,要不然可能結果和預期的結果不同,
當然也可以用year函數來實現
select name, case when year(birthday) > 1988 then 'yong' when year(birthday) < 1980 then 'old' else 'ok' END from lee; ========================================================== create table penalties ( paymentno INTEGER not NULL, payment_date DATE not null, amount DECIMAL(7,2) not null, primary key(paymentno) ) insert into penalties values(1,'2008-01-01',3.45); insert into penalties values(2,'2009-01-01',50.45); insert into penalties values(3,'2008-07-01',80.45);
第一題:對罰款登記分為三類,第一類low,包括大於0小於等於40的罰款,第二類moderate大於40到80之間的罰款,第三類high包含所有大於80的罰款
select payment_date, amount, case when amount >= 0 AND amount < 40 then 'low' when amount >=40 AND amount < 80 then 'moderate' when amount >=80 then 'high' else 'null' END FROM penalties
第二題:統計出屬於low的罰款編號
select * from ( select paymentno, amount, case when amount >= 0 AND amount < 40 then 'low' when amount >=40 AND amount < 80 then 'moderate' when amount >=80 then 'high' else 'incorrect' end lvl from penalties) as p where p.lvl = 'low'
PS:Mysql,Case When,Case多個字段
select distinct a.PatientID,a.PatientCode,a.PatientSex,a.MobileNo,a.HomePhoneNo,a.UserAge,a.PatientName,a.PatientIDCard, DATE_FORMAT(a.RegistDate,'%Y-%m-%d') as RegistDate, case when b.usedstartTime is not null and b.UsedEndTime is null then '1' when b.usedstartTime is not null and b.UsedEndTime is not null then '2' end as 'usedState' from mets_v_patient_baseinfo a left join mets_devices_used_history b on a.patientid = b.PatientID where (select ifnull(IsDeleted,0) from userpublic_info where UserID = a.PatientID ) = 0 and 1=1 order by PatientID Desc limit 0,15