最近又碰到行專列問題了,當時不假思索用的是子查詢,作完後我詢問面試管行專列標正的寫法應該如何寫,他告訴我說應該用"Decode",索性我就總結一下,一共三種方式
--=========建表語句
CREATE TABLE populations(
country VARCHAR2(20),
sex INT,
populcation INT
);
--=========插入記錄
insert into populations (COUNTRY, SEX, POPULCATION)
values ('中國 ', 1, 340);
insert into populations (COUNTRY, SEX, POPULCATION)
values ('中國 ', 2, 260);
insert into populations (COUNTRY, SEX, POPULCATION)
values ('美國 ', 1, 45);
insert into populations (COUNTRY, SEX, POPULCATION)
values ('美國 ', 2, 55);
insert into populations (COUNTRY, SEX, POPULCATION)
values ('加拿大', 1, 51);
insert into populations (COUNTRY, SEX, POPULCATION)
values ('加拿大', 2, 49);
insert into populations (COUNTRY, SEX, POPULCATION)
values ('英國 ', 1, 40);
insert into populations (COUNTRY, SEX, POPULCATION)
values ('英國 ', 2, 60);
commit;
--=========三種方式
--------------------------------------
Decode 方式
SELECT a.COUNTRY AS "國家",
SUM(DECODE(a.SEX, 1, a.POPULCATION)) AS "男",
SUM(DECODE(a.SEX, 2, a.POPULCATION)) AS "女"
FROM populations a
GROUP BY a.COUNTRY
--------------------------------------
Case When 方式
SELECT a.COUNTRY AS "國家",
SUM(CASE
WHEN a.SEX = 1 THEN
a.POPULCATION
END) AS "男",
SUM(CASE
WHEN a.SEX = 2 THEN
a.POPULCATION
END) AS "女"
FROM populations a
GROUP BY a.COUNTRY
--------------------------------------
PIVOT 方式 11G特有的方式
SELECT *
FROM (SELECT a.COUNTRY AS "國家", a.SEX, a.POPULCATION FROM populations a)
PIVOT(
SUM(POPULCATION)
FOR SEX IN(1 AS "男",2 AS "女")) 面試