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Hash join: Difference between revisions
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28 4 Glory 35 Buffy
</pre>
=={{header|Oberon-2}}==
Works with oo2c version 2
<lang oberon2>
MODULE HashJoin;
IMPORT
ADT:Dictionary,
ADT:LinkedList,
NPCT:Tools,
Object,
Object:Boxed,
Out;
TYPE
(* Some Aliases *)
Age= Boxed.LongInt;
Name= STRING;
Nemesis= STRING;
(* Generic Tuple *)
Tuple(E1: Object.Object; E2: Object.Object) = POINTER TO TupleDesc(E1,E2);
TupleDesc(E1: Object.Object; E2: Object.Object) = RECORD
(Object.ObjectDesc)
_1: E1;
_2: E2;
END;
(* Relations *)
RelationA = ARRAY 5 OF Tuple(Age,Name);
RelationB = ARRAY 5 OF Tuple(Name,Nemesis);
VAR
tableA: RelationA;
tableB: RelationB;
dict: Dictionary.Dictionary(Name,LinkedList.LinkedList(Age));
ll: LinkedList.LinkedList(Age);
PROCEDURE (t: Tuple(E1, E2)) INIT*(e1: E1; e2: E2);
BEGIN
t._1 := e1;
t._2 := e2;
END INIT;
PROCEDURE DoHashPhase(t: RelationA;VAR dict: Dictionary.Dictionary(Name,LinkedList.LinkedList(Age)));
VAR
i: INTEGER;
ll: LinkedList.LinkedList(Age);
BEGIN
i := 0;
WHILE (i < LEN(t)) & (t[i] # NIL) DO
IF (dict.HasKey(t[i]._2)) THEN
ll := dict.Get(t[i]._2);
ELSE
ll := NEW(LinkedList.LinkedList(Age));
dict.Set(t[i]._2,ll)
END;
ll.Append(t[i]._1);
INC(i)
END
END DoHashPhase;
PROCEDURE DoJoinPhase(t: RelationB; dict: Dictionary.Dictionary(Name,LinkedList.LinkedList(Age)));
VAR
i: INTEGER;
age: Age;
iterll: LinkedList.Iterator(Age);
BEGIN
FOR i := 0 TO LEN(t) - 1 DO
ll := dict.Get(t[i]._1);
iterll := ll.GetIterator(NIL);
WHILE iterll.HasNext() DO
age := iterll.Next();
Out.LongInt(age.value,4);
Out.Object(Tools.AdjustRight(t[i]._1,10));
Out.Object(Tools.AdjustRight(t[i]._2,10));Out.Ln
END
END
END DoJoinPhase;
BEGIN
(* tableA initialization *)
tableA[0] := NEW(Tuple(Age,Name),NEW(Age,27),"Jonah");
tableA[1] := NEW(Tuple(Age,Name),NEW(Age,18),"Alan");
tableA[2] := NEW(Tuple(Age,Name),NEW(Age,28),"Glory");
tableA[3] := NEW(Tuple(Age,Name),NEW(Age,18),"Popeye");
tableA[4] := NEW(Tuple(Age,Name),NEW(Age,28),"Alan");
(* tableB initialization *)
tableB[0] := NEW(Tuple(Name,Nemesis),"Jonah","Whales");
tableB[1] := NEW(Tuple(Name,Nemesis),"Jonah","Spiders");
tableB[2] := NEW(Tuple(Name,Nemesis),"Alan","Ghost");
tableB[3] := NEW(Tuple(Name,Nemesis),"Alan","Zombies");
tableB[4] := NEW(Tuple(Name,Nemesis),"Glory","Buffy");
dict := NEW(Dictionary.Dictionary(Name,LinkedList.LinkedList(Age)));
DoHashPhase(tableA,dict);
DoJoinPhase(tableB,dict);
END HashJoin.
</lang>
Output:
<pre>
27 Jonah Whales
27 Jonah Spiders
18 Alan Ghost
28 Alan Ghost
18 Alan Zombies
28 Alan Zombies
28 Glory Buffy
</pre>
=={{header|OCaml}}==
This exploits the fact that Hashtbl implements a hash table that can store multiple values for a key, for an especially simple solution:
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