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Video of Ch.03-14 - Reduce Side Join Map Reduce Hadoop in Apache Hadoop course by Garage Education channel, video No. 14 free certified online
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Important Note: at min 21:44 If we need to create left outer join and output only the keys if and only if these keys are available on the customer transaction we have to move Line 49 (context.write) inside the if conditions in Lines 42 && 44. This is a minor bug inside the code. We can do it in many ways better than this, but this for simplicity.
```java
for (String trnx : trnxs) {
if (trnx ! null && cellLKP ! null) {
outputJoin trnx + DATA_SEPARATOR + cellLKP;
context.write(key, new Text(outputJoin));
} else if (cellLKP null) {
outputJoin trnx + DATA_SEPARATOR + UNKNOWN_CELL;
context.write(key, new Text(outputJoin));
}
}
```
In this episode, we explain the following topics.
- Joining in Map Reduce.
- How to implement the reduce side join using the map reduce framework?
Github Code: https://github.com/garage-education/hadoop-map-reduce/tree/main/src/main/java/mr07/reduce_side_join
Lecture Notes: https://gability.com/en/courses/hadoop/05-map-reduce/
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"Big Data Engineering in Depth": https://gability.com/en/courses/big-data-in-depth/
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