Problem Statement

An inner join is an operation that combines two data tables into one table, based on matching column values. The simplest way of implementing this operation is the nested loop join algorithm, but a more scalable alternative is the hash join algorithm. Implement the "hash join" algorithm, and demonstrate that it passes the test-case listed below. You should represent the tables as data structures that feel natural in your programming language. The "hash join" algorithm consists of two steps:

In pseudo-code, the algorithm could be expressed as follows: The order of the rows in the output table is not significant. If you're using numerically indexed arrays to represent table rows (rather than referring to columns by name), you could represent the output rows in the form [[27, "Jonah"], ["Jonah", "Whales"]].

Let's start with the solution:

LeftRec := RECORD
  UNSIGNED1 Age;
  STRING6   Name;
END;

LeftFile := DATASET([{27,'Jonah'},{18,'Alan'},{28,'Glory'},{18,'Popeye'},{28,'Alan'}],LeftRec);

RightRec := RECORD
  STRING6   Name;
  STRING7   Nemesis;
END;
	
RightFile := DATASET([{'Jonah','Whales'},{'Jonah','Spiders'},{'Alan','Ghosts'},{'Alan','Zombies'},{'Glory','Buffy'}],
                     RightRec);
										 
HashJoin := JOIN(LeftFile,RightFile,Left.Name = RIGHT.Name,HASH);

HashJoin;


//The HASH JOIN is built-in to the ECL JOIN by using the HASH JOIN Flag

/*
OUTPUT:
Age Name  Nemesis
18  Alan  Ghosts 
18  Alan  Zombies
28  Alan  Ghosts 
28  Alan  Zombies
28  Glory Buffy  
27  Jonah Whales 
27  Jonah Spiders
*/