Question

oracle group by 2列 怎么分组的

Answer 1

首先按照2列进行排序，相同的作为一组，比如：

按性别和所在系分组后：

Answer 2

先按照第一列进行分组，再按照第二列进行分组，举例如下：
SELECT ID, NAME, SUM(NUM)
FROM (SELECT 1 AS ID, 'A' AS NAME, 12 AS NUM
FROM DUAL
UNION ALL
SELECT 2 AS ID, 'E' AS NAME, 13 AS NUM
FROM DUAL
UNION ALL
SELECT 2 AS ID, 'A' AS NAME, 14 AS NUM
FROM DUAL
UNION ALL
SELECT 2 AS ID, 'A' AS NAME, 11 AS NUM
FROM DUAL
UNION ALL
SELECT 3 AS ID, 'A' AS NAME, 16 AS NUM
FROM DUAL
UNION ALL
SELECT 3 AS ID, 'D' AS NAME, 19 AS NUM
FROM DUAL
UNION ALL
SELECT 3 AS ID, 'E' AS NAME, 15 AS NUM FROM DUAL) A
GROUP BY ID, NAME
ORDER BY ID, NAME

Answer 3

两列一样的进行分组
例如：t表
id name age
1 张三 10
2 李四 20
3 王五 30
4 张三 10
select name ,age from t group by name,age;
上面的查询按照name,age 两列进行分组，分组查询结果
name age
张三 10
李四 20
王五 30