Impala中多列转为一行

之前有一位朋友咨询我，Impala中怎样实现将多列转为一行，事实上Impala中自带函数能够实现，不用自己定义函数。

以下我開始演示：

-bash-4.1$ impala-shell

Starting Impala Shell without Kerberos authentication

Connected to cdha:21000

Server version: impalad version 1.4.2-cdh5 RELEASE (build eac952d4ff674663ec3834778c2b981b252aec78)

Welcome to the Impala shell. Press TAB twice to see a list of available commands.





Copyright (c) 2012 Cloudera, Inc. All rights reserved.

(Shell build version: Impala Shell v1.4.2-cdh5 (eac952d) built on Tue Sep 16 19:15:40 PDT 2014)

[cdha:21000] > create table student(name string,subject string,score decimal(4,1));    -------------创建演示表：student(脱离学校四年了。还不忘自己是学生^_^)

Query: create table student(name string,subject string,score decimal(4,1))





Returned 0 row(s) in 1.97s

[cdha:21000] > insert into student values('xiaoming','math',89.5); ----------------插入演示数据 (小明和花花的学习成绩，他们感情比較好)

Query: insert into student values('xiaoming','math',89.5)

Inserted 1 rows in 2.56s

[cdha:21000] > insert into student values('xiaoming','english',92);

Query: insert into student values('xiaoming','english',92)

Inserted 1 rows in 0.39s

[cdha:21000] > insert into student values('xiaoming','chinese',98);

Query: insert into student values('xiaoming','chinese',98)

Inserted 1 rows in 0.42s

[cdha:21000] > insert into student values('huahua','chinese',80);

Query: insert into student values('huahua','chinese',80)

Inserted 1 rows in 0.40s

[cdha:21000] > insert into student values('huahua','math',89.5);

Query: insert into student values('huahua','math',89.5)

Inserted 1 rows in 0.29s

[cdha:21000] > select * from student;    ----------每次考完试，老师报分数时都非常紧张    

Query: select * from student

+----------+---------+-------+

| name     | subject | score |

+----------+---------+-------+

| xiaoming | english | 92.0  |

| huahua   | chinese | 80.0  |

| xiaoming | chinese | 98.0  |

| huahua   | math    | 89.5  |

| xiaoming | math    | 89.5  |

+----------+---------+-------+

Returned 5 row(s) in 0.23s





[cdha:21000] > select name,group_concat(subject,',') from student group by  name;  ------------小试牛刀，看到了吧，多列拼接到一起了

Query: select name,group_concat(subject,',') from student group by  name

+----------+----------------------------+

| name     | group_concat(subject, ',') |

+----------+----------------------------+

| xiaoming | english,chinese,math       |

| huahua   | chinese,math               |

+----------+----------------------------+

Returned 2 row(s) in 0.38s

------------以下演示有价值的演示样例，显示高手之招，呵呵

------------这样就能够在一行上面，看到小明和花花的各科成绩了

[cdha:21000] > select name,group_concat(concat_ws('=',subject,cast(score as string)),',') from student group by  name;  

Query: select name,group_concat(concat_ws('=',subject,cast(score as string)),',') from student group by  name

+----------+-------------------------------------------------------------------+

| name     | group_concat(concat_ws('=', subject, cast(score as string)), ',') |

+----------+-------------------------------------------------------------------+

| xiaoming | english=92.0,chinese=98.0,math=89.5                               |

| huahua   | chinese=80.0,math=89.5                                            |

+----------+-------------------------------------------------------------------+

Returned 2 row(s) in 0.39s

[cdha:21000] >

Hive的行列转换请查看： http://blog.csdn.net/jiangshouzhuang/article/details/46810529