Pig : CoGroup examples Vs Union Examples

-- co groupinggrunt> cat piglab/emp101,aaaa,40000,m,11102,bbbbbb,50000,f,12103,cccc,50000,m,12104,dd,90000,f,13105,ee,10000,m,12106,dkd,40000,m,12107,sdkfj,80000,f,13108,iiii,50000,m,11grunt>[cloudera@quickstart ~]$ cat > emp2201,Ravi,80000,m,12203,Varuna,100000,f,13204,Vanila,50000,f,12205,Mani,30000,m,14206,Manisha,30000,f,14[cloudera@quickstart ~]$ hadoop fs -copyFromLocal emp2 piglab[cloudera@quickstart ~]$ sql:   select dno, sum(sal) from (      select dno, sal from emp1              union all      select dno, sal from emp2       ) e group by dno;runt> emp1 = load 'piglab/emp' using      PigStorage(',')    as (id:int, name:chararray, sal:int,    sex:chararray,      dno:int);grunt> emp2 = load 'piglab/emp2' using PigStorage(',')    as (id:int, name:chararray, sal:int,    sex:chararray,     dno:int);grunt> describe emp1emp1: {id: int,name: chararray,sal: int,sex:chararray,dno: int}grunt> describe emp2emp2: {id: int,name: chararray,sal: int,sex:chararray,dno: int}grunt> e1 = foreach emp1 generate dno, sal;grunt> e2 = foreach emp2 generate dno, sal;grunt> e = union e1, e2;grunt> grp = group e by dno;grunt> res = foreach grp generate group as dno,               SUM(e.sal) as tot;grunt> dump res(11,180000)(12,280000)(13,270000)(14,60000) -- in above output,    we missed clarity,    total salary for branch1 and brach2    above is the aggregation of all branches. -- we want,   seperate total salary for branch 1 and   seperate for branch2. -- for this cogroup is used.  -- cogroup  will construct seperate     innerbags for each relation(dataset).   so that seperate aggregations, we can apply.grunt> describe e1e1: {dno: int,sal: int}grunt> describe e2e2: {dno: int,sal: int}grunt> cg = cogroup e1 by dno, e2 by dno;grunt> describe cgcg: {group: int,e1: {(dno: int,sal: int)},e2:{(dno: int,sal: int)}}grunt> dump cg -- when cogroup is applied it returns  n+1 fields .  where n is number of input relations   (datasets).   first one is group   2nd onwards bags.(11,{(11,50000),(11,40000)},{(11,90000)})(12,{(12,40000),(12,10000),(12,50000),(12,50000)},{(12,50000),(12,80000)})(13,{(13,80000),(13,90000)},{(13,100000)})(14,{},{(14,30000),(14,30000)})grunt> res = foreach cg generate        group as dno ,         SUM(e1.sal) as tot1,         SUM(e2.sal) as tot2;grunt> describe resres: {dno: int,tot1: long,tot2: long}(11,90000,90000)(12,150000,130000)(13,170000,100000)(14,,60000)---------------------------------  how to perform,    seperate aggregations on each dataset  with out cogrouping.grunt> describe e1e1: {dno: int,sal: int}grunt> describe e2e2: {dno: int,sal: int}grunt> ee1 = foreach e1 generate *, 'branch1' asbranch;grunt> ee2 = foreach e2 generate *, 'branch2' asbranch;grunt> ee = union ee1 , ee2;grunt> grp = group ee by (dno, branch);grunt> res = foreach grp generate>>         group.dno as dno, group.branch asbranch,>>              SUM(ee.sal) as tot;grunt> describe resres: {dno: int,branch: chararray,tot: long}grunt> dump res(11,branch1,90000)(11,branch2,90000)(12,branch1,150000)(12,branch2,130000)(13,branch1,170000)(13,branch2,100000)(14,branch2,60000)--------------------------------- using Cogroup , multiple aggregations  seperately for each dataset.grunt> describe e1e1: {dno: int,sal: int}grunt> describe e2;e2: {dno: int,sal: int}grunt> cg = cogroup e1 by dno, e2 by dno;grunt> res = foreach cg generate>>     group as dno,>>     SUM(e1.sal) as tot1,>>     SUM(e2.sal) as tot2,>>     COUNT(e1) as cnt1,>>     COUNT(e2) as cnt2,>>     MAX(e1.sal) as max1,>>     MAX(e2.sal) as max2;grunt> describe res;res: {dno: int,tot1: long,tot2: long,cnt1:long,cnt2: long,max1: int,max2: int}grunt> dump res(11,90000,90000,2,1,50000,90000)(12,150000,130000,4,2,50000,80000)(13,170000,100000,2,1,90000,100000)(14,,60000,0,2,,30000)------------------------------   Entire Column aggregations using CoGroup. s1 = foreach emp1 generate sal; s2 = foreach emp2 generate sal; g = cogroup s1  all, s2 all ; r = foreach g generate      SUM(s1.sal) as tot1,       SUM(s2.sal) as tot2; r = foreach r generate * , tot1+tot2 as tot;dump r(410000,380000,790000)