hive一行資料中一列拆分成多行
lateral view用於和split、explode等UDTF一起使用的，能將一行資料拆分成多行資料，在此基礎上可以對拆分的資料進行聚合，lateral view首先為原始表的每行呼叫UDTF，UDTF會把一行拆分成一行或者多行，lateral view在把結果組合，產生一個支援別名表的虛擬表。
單個LATERAL VIEW:
源表（table1）資料{A:string B:array<BIGINT> C:string}
A B C
190 [1030,1031,1032,1033,1190] select id
191 [1030,1031,1032,1033,1190] select id
希望的結果是：
190 1030 select id
190 1031 select id
190 1032 select id
190 1033 select id
190 1190 select id
191 1030 select id
191 1031 select id
191 1032 select id
191 1033 select id
191 1190 select id
故使用select A,B,C from table_1 LATERAL VIEW explode(B) table1 as B得到上述結果
多個LATERAL VIEW的介紹：
LATERAL VIEW clauses are applied in the order that they appear. For example with the following base table:
|
Array<int> col1 |
Array<string> col2 |
|
[1, 2] |
[a", "b", "c"] |
|
[3, 4] |
[d", "e", "f"] |
SELECT myCol1, myCol2 FROM baseTable
LATERAL VIEW explode(col1) myTable1 AS myCol1
LATERAL VIEW explode(col2) myTable2 AS myCol2;
結果如下：
|
int myCol1 |
string myCol2 |
|
1 |
"a" |
|
1 |
"b" |
|
1 |
"c" |
|
2 |
"a" |
|
2 |
"b" |
|
2 |
"c" |
|
3 |
"d" |
|
3 |
"e" |
|
3 |
"f" |
|
4 |
"d" |
|
4 |
"e" |
|
4 |
"f" |
複雜方式：
select * from tb_split;
20141018 aa|bb 7|9|0|3
20141019 cc|dd 6|1|8|5
使用方式：select datenu,des,type from tb_split
lateral view explode(split(des,"//|")) tb1 as des
lateral view explode(split(type,"//|")) tb2 as type
執行過程是先執行from到 as cloumn的列過程，在執行select 和where後邊的語句；