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;
在這里用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'