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matthayes/left_joins.pig

Created August 8, 2013 20:46
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When joining on more than two relations, one option is to use multiple joins. However this means multiple MapReduce jobs, which is inefficient.
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left_joins.pig
input1 = LOAD 'input1' using PigStorage(',') AS (val1:INT,val2:INT);
input2 = LOAD 'input2' using PigStorage(',') AS (val1:INT,val2:INT);
input3 = LOAD 'input3' using PigStorage(',') AS (val1:INT,val2:INT);
data1 = JOIN input1 BY val1 LEFT, input2 BY val1;
data1 = FILTER data1 BY input1::val1 IS NOT NULL;
data2 = JOIN data1 BY input1::val1 LEFT, input3 BY val1;
data2 = FILTER data2 BY input1::val1 IS NOT NULL;
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