sql学习~pivot和unpivot用法

pivot 

可以把列值转换为输出中的多个列。

pivot 可以在其他剩余的列的值上执行聚合函数。

unpivot

将列转换为列值

语法

SELECT <non-pivoted column>,
    [first pivoted column] AS <column name>,
    [second pivoted column] AS <column name>,
    ...
    [last pivoted column] AS <column name>
FROM
    (<SELECT query that produces the data>)
    AS <alias for the source query>
PIVOT
(
    <aggregation function>(<column being aggregated>)
FOR
[<column that contains the values that will become column headers>]
    IN ( [first pivoted column], [second pivoted column],
    ... [last pivoted column])
) AS <alias for the pivot table>
<optional ORDER BY clause>;

示例1：pivot

1.数据准备

create table student_score
(
    studentId varchar(50),
    subjectName varchar(50),
    score decimal(18)
)

insert into student_score values
('','语文',80),('','数学',70),('','英语',90),
('','语文',80),('','数学',83),('','英语',60),
('','语文',50),('','数学',90),('','英语',60),
('','语文',90),('','数学',80)

按学生id分组查看平均成绩

select studentId,AVG(score) avgScore from student_score
group by studentId

初始效果

2.使用pivot

select 'averagescore' as avgScore_by_studentId,
[],[],[],[]
from
(
select studentId,score
    from student_score
) as sourceTable
pivot
(
AVG(score) for studentId in ([],[],[],[])
) as pivotTable

3.效果

示例2：unpivot 

1.数据准备

-- Create the table and insert values as portrayed in the previous example.
CREATE TABLE pvt (VendorID int, Emp1 int, Emp2 int,
    Emp3 int, Emp4 int, Emp5 int);
GO
INSERT INTO pvt VALUES (1,4,3,5,4,4);
INSERT INTO pvt VALUES (2,4,1,5,5,5);
INSERT INTO pvt VALUES (3,4,3,5,4,4);
INSERT INTO pvt VALUES (4,4,2,5,5,4);
INSERT INTO pvt VALUES (5,5,1,5,5,5);
GO 

初始效果

表示供应商(vendorID)在用户1(Emp1)中的订单数量，其他类比即可。

2.使用示例

-- Unpivot the table.
SELECT VendorID, Employee, Orders
FROM
   (SELECT VendorID, Emp1, Emp2, Emp3, Emp4, Emp5
   FROM pvt) p
UNPIVOT
   (Orders FOR Employee IN
      (Emp1, Emp2, Emp3, Emp4, Emp5)
)AS unpvt;  

3.效果

参考网址