hive 实现 udf row_number 以及遇到的问题
为hive的每条数据添加row_number, 首先添加行号，必须考虑到数据必须放在一个reduce中去执行。先上代码
package xx.xxxxx.hive.udf;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.ql.udf.UDFType;
@UDFType(deterministic = false)
public class RowNumber extends UDF {
private static int MAX_VALUE = 50;
private static String comparedColumn[] = new String[MAX_VALUE];
private static int rowNum = 1;
public int evaluate(Object ...args) {
String columnValue[] = new String[args.length];
for (int i = 0; i < args.length; i++){
columnValue[i] = args[i].toString();
}
if (rowNum == 1) {
for (int i = 0; i < columnValue.length; i++)
comparedColumn[i] = columnValue[i];
}
for (int i = 0; i < columnValue.length; i++) {
if (!comparedColumn[i].equals(columnValue[i])) {
for (int j = 0; j < columnValue.length; j++) {
comparedColumn[j] = columnValue[j];
}
rowNum = 1;
return rowNum++;
}
}
return rowNum++;
}
}
打包jar包，并创建函数。
add jar /home/hdbatch/jars/iclickhiveudf.jar;
create temporary function row_number as 'cn.iclick.hive.udf.RowNumber';
但是用法要注意，假设我要对一个表的数据进行标注行号，两条sql语句，
create table test_tony as select row_number(1), tid from(select distinct tid from cookie where i_date=20131105)t order by tid;
上边这条语句会标注行号错误，会产生11个reduce，所以会打11份相同的row number，所以就会有错误，为什么会有不同的解释呢？？？ 看explain sql语句， 原因是
编写non-deterministic的UDF时遇到的谓词下推错误。
具体详见： http://blog.sina.com.cn/s/blog_6ff05a2c01017myn.html
正确的写法：
create table test_tony as select row_number(1) rownumber, tid from (select distinct tid from cookie where i_date=20131105 order by tid) t ;（一）
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-2 depends on stages: Stage-1
Stage-0 is a root stage
STAGE PLANS:
Stage: Stage-1
Map Reduce
Alias -> Map Operator Tree:
t:cookie_label_weight
TableScan
alias: cookie_label_weight
Select Operator
expressions:
expr: tid
type: string
outputColumnNames: tid
Group By Operator
bucketGroup: false
keys:
expr: tid
type: string
mode: hash
outputColumnNames: _col0
Reduce Output Operator
key expressions:
expr: _col0
type: string
sort order: +
Map-reduce partition columns:
expr: _col0
type: string
tag: -1
Reduce Operator Tree:
Group By Operator
bucketGroup: false
keys:
expr: KEY._col0
type: string
mode: mergepartial
outputColumnNames: _col0
Select Operator
expressions:
expr: _col0
type: string
outputColumnNames: _col0
Select Operator
expressions:
expr: row_number(1)
type: int
expr: _col0
type: string
type: int
expr: _col0
type: string
outputColumnNames: _col0, _col1
File Output Operator
compressed: false
GlobalTableId: 0
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
Stage: Stage-2
Map Reduce
Alias -> Map Operator Tree:
maprfs:/user/hdbatch/tmp/hive/hive_2013-11-08_18-13-02_418_6171072878206847672/-mr-10002
Reduce Output Operator
key expressions:
expr: _col1
type: string
sort order: +
tag: -1
value expressions:
expr: _col0
type: int
expr: _col1
type: string
Reduce Operator Tree:
Extract
File Output Operator
compressed: false
GlobalTableId: 0
table:
input format: org.apache.hadoop.mapred.TextInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
Stage: Stage-0
Fetch Operator
limit: -1
（二）
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-2 depends on stages: Stage-1
Stage-0 is a root stage
STAGE PLANS:
Stage: Stage-1
Map Reduce
Alias -> Map Operator Tree:
t:cookie_label_weight
TableScan
alias: cookie_label_weight
Select Operator
expressions:
expr: tid
type: string
outputColumnNames: tid
Group By Operator
bucketGroup: false
keys:
expr: tid
type: string
mode: hash
outputColumnNames: _col0
Reduce Output Operator
key expressions:
expr: _col0
type: string
sort order: +
Map-reduce partition columns:
expr: _col0
type: string
tag: -1
Reduce Operator Tree:
Group By Operator
bucketGroup: false
keys:
expr: KEY._col0
type: string
mode: mergepartial
outputColumnNames: _col0
Select Operator
expressions:
expr: _col0
type: string
outputColumnNames: _col0
File Output Operator
compressed: false
GlobalTableId: 0
table:
input format: org.apache.hadoop.mapred.SequenceFileInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
Stage: Stage-2
Map Reduce
Alias -> Map Operator Tree:
maprfs:/user/hdbatch/tmp/hive/hive_2013-11-08_18-02-33_734_4047092562620720785/-mr-10002
Reduce Output Operator
key expressions:
expr: _col0
type: string
sort order: +
tag: -1
value expressions:
expr: _col0
type: string
Reduce Operator Tree:
Extract
Select Operator
expressions:
expr: row_number(1)
type: int
expr: _col0
type: string
outputColumnNames: _col0, _col1
File Output Operator
compressed: false
GlobalTableId: 0
table:
input format: org.apache.hadoop.mapred.TextInputFormat
output format: org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
Stage: Stage-0
Fetch Operator
limit: -1