Write mapreduce code to search for pattern - hadoop

Question

customer_id, server_id, code
12342344, 1232, 3
12345456, 1433, 2
16345436, 2343, 4
12245456, 1434, 3
11145456, 1436, 2
If I'm running this query on hive:
select * from table where code=3;
what would be the code written in mapreduce, where can I find it ?
in another word, how can I write mapreduce job to give the same query results above ?
Thanks

Answer 1

you can run EXPLAIN select * from table where code=3; from hive to see hive's query execution plan, but hive doesn't output any mapreduce code for any query. Also check YSmart-Another SQL-to-MapReduce Translator - to see mapreduce jobs for SQL - I never used it, but you can try it out:
This is sample, you can try to modify for different other queries to get an idea . Basically you will filter the data in map class and run some aggregations in reduce class. but in this example you don't need reduce class as it is simple mapping from data. You will need to go through wordcount (helloworld example of hadooop) first in order to learn how to run this program and where to find output etc.
Output:
12245456, 1434, 3
12342344, 1232, 3
Code:
public class customers{
public static class customersMapper extends Mapper<Object, Text, Text, Text> {
#Override
public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
//this code should be converted to Int - try it for your self
String code = value.toString().split(",")[2].trim();
//this line should be chnaged if code variable is converted to Int
if (code.equals("3")){ // only map rec where code=3
context.write(value,new Text(""));
}
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "get-customer-with-code=3");
job.setJarByClass(customers.class);
job.setMapperClass(customersMapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.waitForCompletion(true);
}
}