apache - 有没有办法在配置单元 UDF 中获取数据库名称

Question

我正在编写 Hive UDF。

我必须获取数据库的名称(函数部署在其中)。然后，我需要根据数据库环境从 hdfs 访问一些文件。你能帮我看看哪个函数可以帮助从 Hive UDF 运行 HQL 查询吗？

Answer 1

1. 编写UDF类并准备jar文件

public class MyHiveUdf extends UDF {
    public Text evaluate(String text,String dbName) {
        if(text == null) {
            return null;
        } else {
              return new Text(dbName+"."+text);
        }
    }
}

1. 像下面提到的那样在 hive 查询中使用这个 UDF

hive > 使用 mydb； 好的 耗时:0.454秒

hive> ADD jar /root/MyUdf.jar;
Added [/root/MyUdf.jar] to class path
Added resources: [/root/MyUdf.jar]

hive> create temporary function myUdfFunction as 'com.hiveudf.strmnp.MyHiveUdf';
OK
Time taken: 0.018 seconds

hive> select myUdfFunction(username,current_database()) from users;
Query ID = root_20170407151010_2ae29523-cd9f-4585-b334-e0b61db2c57b
Total jobs = 1
Launching Job 1 out of 1
Number of reduce tasks is set to 0 since there's no reduce operator
Starting Job = job_1491484583384_0004, Tracking URL = http://mac127:8088/proxy/application_1491484583384_0004/
Kill Command = /opt/cloudera/parcels/CDH-5.9.0-1.cdh5.9.0.p0.23/lib/hadoop/bin/hadoop job  -kill job_1491484583384_0004
Hadoop job information for Stage-1: number of mappers: 1; number of reducers: 0
2017-04-07 15:11:11,376 Stage-1 map = 0%,  reduce = 0%
2017-04-07 15:11:19,766 Stage-1 map = 100%,  reduce = 0%, Cumulative CPU 3.12 sec
MapReduce Total cumulative CPU time: 3 seconds 120 msec
Ended Job = job_1491484583384_0004
MapReduce Jobs Launched:
Stage-Stage-1: Map: 1   Cumulative CPU: 3.12 sec   HDFS Read: 21659 HDFS Write: 381120 SUCCESS
Total MapReduce CPU Time Spent: 3 seconds 120 msec
OK

mydb.user1
mydb.user2
mydb.user3

Time taken: 2.137 seconds, Fetched: 3 row(s)
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