表的创建

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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

数据插入：

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123	`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');`

第一种用法:

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SELECT name, CASE WHEN birthday '1981' THEN 'old'WHEN birthday > '1988' THEN 'yong' ELSE 'ok' END YORNFROM lee

第二种用法：

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SELECT NAME, CASE name WHEN 'sam' THEN 'yong' WHEN 'lee' THEN 'handsome' ELSE 'good' END as oldnameFROM lee

第三种：当然了，case when 语句还可以复合

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select name, birthday, casewhen birthday > '1983' then 'yong' when name='lee' then 'handsome' else 'just so so' endfrom lee;

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

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select name, case when year(birthday) > 1988 then 'yong' when year(birthday) then 'old' else 'ok' ENDfrom 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

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select payment_date, amount, casewhen amount >= 0 AND amount then 'low' when amount >=40 AND amount then 'moderate' when amount >=80 then 'high'else 'null' ENDFROM penalties

第二题:统计出属于low的罚款编号

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select * from( select paymentno, amount, casewhen amount >= 0 AND amount then 'low' when amount >=40 AND amount then 'moderate' when amount >=80 then 'high'else 'incorrect' end lvl from penalties) as pwhere p.lvl = 'low'

PS：Mysql，Case When,Case多个字段

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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

ITPub博客

详解Mysql case then使用

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