方法一: 如果对case when的查询结果起别名,一定要放在end之后。
SELECT username,amount,
WHEN 1 THEN '申请中'
WHEN 2 THEN '被锁定'
WHEN 3 THEN '已同意'
ELSE '已取消' END STATUS
FROM application;
方法二:
SELECT
CASE WHEN STATE = '1' THEN '成功'
WHEN STATE = '2' THEN '失败'
ELSE '其他' END
FROM SYS_SCHEDULER
例如:
有员工表empinfo
(
Fempno varchar2(10) not null pk,
Fempname varchar2(20) not null,
Fage number not null,
Fsalary number not null
);
假如数据量很大约1000万条;写一个你认为最高效的SQL,用一个SQL计算以下四种人:
fsalary>9999 and fage > 35
fsalary>9999 and fage < 35
fsalary <9999 and fage > 35
fsalary <9999 and fage < 35
每种员工的数量;
select sum(case when fsalary > 9999 and fage > 35
then 1
else 0end) as "fsalary>9999_fage>35",
sum(case when fsalary > 9999 and fage < 35
then 1
else 0
end) as "fsalary>9999_fage<35",
sum(case when fsalary < 9999 and fage > 35
then 1
else 0
end) as "fsalary<9999_fage>35",
sum(case when fsalary < 9999 and fage < 35
then 1
else 0
end) as "fsalary<9999_fage<35"
from empinfo;