hive使用笔记

ALTER TABLE table1 DROP PARTITION (day='2015-07-14');

ALTER TABLE table1 ADD COLUMNS (visit int); 

解码url

reflect("java.net.URLDecoder", "decode", url,"UTF-8")

CASE WHEN  b.user_account is null then 0 else b.user_account end

parse_url(concat(uri), 'QUERY', 'siteid')    uri必须以http开头，当不存在siteid参数是返回NULL

first_value(a) OVER(PARTITION BY  ORDER BY t.cnt desc)

 sort_array(collect_set(url) OVER(PARTITION BY cookie ORDER BY createtime))

一行转多列

explode(ARRAY)  列表中的每个元素生成一行

explode(MAP) map中每个key-value对，生成一行，key为一列，value为一列

lateral view用于和split, explode等UDTF一起使用，它能够将一行数据拆成多行数据，在此基础上可以对拆分后的数据进行聚合。lateral view首先为原始表的每行调用UDTF，UTDF会把一行拆分成一或者多行，lateral view再把结果组合，产生一个支持别名表的虚拟表。

例如：

SELECT pageid, adid FROM pageAds LATERAL VIEW explode(adid_list) adTable AS adid;

SELECT myCol1, myCol2 FROM baseTable  
    LATERAL VIEW explode(col1) myTable1 AS myCol1  
    LATERAL VIEW explode(col2) myTable2 AS myCol2;  

多列转一行

select max(ubi.id), ubi.name, concat_ws(',', collect_set(ua.address)) as address from user_basic_info ubi join user_address ua on ubi.name=ua.name group by ubi.name;