Hive建立外部表与时间戳转换（含建dual表，修改列名，row_number() 函数等）

建外部表，之前hadoop职位统计就是这么做的

hive> drop table job;OKTime taken: 5.446 secondshive> show tables;OKTime taken: 0.018 secondshive> create external table job(area string, experience string, degree string,    > num string, salary string)    > row format delimited fields terminated by ','    > location '/job';#在hdfs先建好这个文件夹，并上传好数据OKTime taken: 0.103 secondshive> select * from job;OK北京3-5年本科3人 15001-20000元/月北京1-3年本科3人 10001-15000元/月杭州3-5年本科1人 15001-20000元/月 。。。hive> select area, count(area) from job group by area;

建表

hive> create external table tctest(uid string,goodsid string,behtype string,space string,category string,time string)hive> row format delimited fields terminated by ','hive> location '/tianchitest';

将日期转化为时间戳

hive> select unix_timestamp(time,'yyyyMMddHH') from tctest;

利用上面的函数+CTAS语句创建一个含时间戳的表

hive> create table tcc as select uid,goodsid,behtype,space,category,unix_timestamp(time,'yyyy-MM-dd HH') from tctest;

最好直接改列名

hive> create table tcc as select uid,goodsid,behtype,space,category,unix_timestamp(time,'yyyy-MM-dd HH') as time from tctest;

dual表

因为Hive里没有自带dual表，所以我们要自己建一个

hive> create table dual(dummy string);#之后建一个dual.txt里面写个值Xhive> load data local inpath '/home/guo/dual.txt' into table dual;hive> select unix_timestamp("2014-12-18 23:59:59") from dual;OK1418918399Time taken: 0.082 seconds, Fetched: 1 row(s)hive> select unix_timestamp("2014-12-17 23:59:59") from dual;OK1418831999Time taken: 0.112 seconds, Fetched: 1 row(s)

将时间戳转化为日期

hive> select from_unixtime(1418831999) from dual;OK2014-12-17 23:59:59Time taken: 0.111 seconds, Fetched: 1 row(s)

查看表结构

hive> describe tcc;OKuid                 string                                  goodsid             string                                  behtype             string                                  space               string                                  category            string                                  _c5                 bigint                                  Time taken: 0.025 seconds, Fetched: 6 row(s)

修改列名，注意那是反引号

hive> alter table tcc change `_c5` time bigint;OKTime taken: 0.172 seconds

将hive表中内容导到本地

guo@guo:~$ hive -e "select * from tcpredict" >> predict.csv

开始的想法奉上（当时没有理解题意，想的也比较简单）

hive> create external table tclx(uid string,goodsid string,behtype string,space string,category string,time string)hive> row format delimited fields terminated by ','hive> location '/tianchilx';hive> create table tianchi as select uid,goodsid,behtype,space,category,unix_timestamp(time,'yyyy-MM-dd HH') as time from tclx;#改列名，不用了hive> alter table tianchi change `_c5` time bigint;

0.0

hive> create table tct1 as select distinct uid from tianchi where behtype = 3 and time > 1418831999;hive> create table tct2 as select t.* from tianchi t,tct1 c where t.uid=c.uid;hive> select * from tct2 limit 5;#查看表的前五行数据hive> create table tct3 as select distinct uid from tct2 where behtype=4; hive> create table tct4 as select t.* from tct2 t,tct3 c where t.uid=c.uid;

改进一下

hive> create table tct6 as select c.* from (select distinct uid from tct2 where behtype=4)t,tct2 c where t.uid=c.uid;

或者，更直接一点

hive> create table tct7 as select c.* from (select distinct uid from (select a.* from tianchi a,(select distinct uid from tianchi where behtype=3 and time>1418831999) b where a.uid=b.uid)t where t.behtype=4)t,tct2 c where t.uid=c.uid

或者，改进一点，用in

hive> create table tct8 as select c.* from (select distinct uid from (select a.* from tianchi a where a.uid in (select distinct uid from tianchi where behtype=3 and time>1418831999))b where b.behtype=4)t,tct2 c where t.uid=c.uid;

再改进一点

hive> create table tct9 as select c.* from tct2 c where c.uid in (select distinct uid from (select a.* from tianchi a where a.uid in (select distinct uid from tianchi where behtype=3 and time>1418831999))b where b.behtype=4);

下面来自：http://jingyan.baidu.com/article/9989c74604a644f648ecfef3.html

简单的说row_number()从1开始，为每一条分组记录返回一个数字，这里的ROW_NUMBER() OVER (ORDER BY xlh DESC) 是先把xlh列降序，再为降序以后的没条xlh记录返回一个序号。 

SELECT *, Row_Number() OVER (partition by deptid ORDER BY salary desc) rank FROM employee

根据部门分组，显示每个部门的工资等级