Mysql实例详解Mysql case then使用

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本文介绍了Mysql实例详解Mysql case then使用，希望对您有用。如果有疑问，可以联系我们。

MYSQL应用表的创建

MYSQL应用
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

MYSQL应用数据插入：

MYSQL应用
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');

MYSQL应用第一种用法:

MYSQL应用
SELECT name,CASE WHEN birthday < '1981' THEN 'old' 
WHEN birthday > '1988' THEN 'yong'
 ELSE 'ok' END YORN
FROM lee

MYSQL应用第二种用法：

MYSQL应用
SELECT NAME,CASE name
 WHEN 'sam' THEN 'yong'
 WHEN 'lee' THEN 'handsome'
 ELSE 'good' END as oldname
FROM lee

MYSQL应用第三种：当然了,case when 语句还可以复合

MYSQL应用
select name,birthday,case 
when birthday > '1983' then 'yong'
 when name='lee' then 'handsome'
 else 'just so so' end
from lee;

MYSQL应用在这里用sql语句进行日期比较的话,需要对年加引号,要不然可能结果和预期的结果不同,
当然也可以用year函数来实现

MYSQL应用
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);

MYSQL应用第一题：对罚款登记分为三类,第一类low,包括大于0小于等于40的罚款,第二类moderate大于40到80之间的罚款,第三类high包含所有大于80的罚款

MYSQL应用
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

MYSQL应用第二题:统计出属于low的罚款编号

MYSQL应用
select * from 
( select paymentno,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'

MYSQL应用PS：Mysql,Case When,Case多个字段

MYSQL应用
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 

（编辑：李大同）

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