natural join and example to test it

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@8 014f5005-505e-4b48-8d0a-63407b615a7c

relation.py

@@ -198,6 +198,46 @@ class relation (object):
 			if e not in newt.content:
 				newt.content.append(list(e))
 		return newt
+	def join(self,other):
+		'''Natural join, using field's names'''
+		shared=[]
+		for i in self.header.fields:
+			if i in other.header.fields:
+				shared.append(i)
+		newt=relation() #Creates the new relation
+		
+		#Adds all the fields of the 1st relation
+		newt.header=header(list(self.header.fields))
+		
+		#Adds all the fields of the 2nd, when non shared
+		for i in other.header.fields:
+			if i not in shared:
+				newt.header.fields.append(i)
+		#Shared ids of self
+		sid=self.header.getFieldsId(shared)
+		#Shared ids of the other relation
+		oid=other.header.getFieldsId(shared)
+		
+		#Non shared ids of the other relation
+		noid=[]
+		for i in range(len(other.header.fields)):
+			if i not in oid:
+				noid.append(i)
+		
+		for i in self.content:
+			for j in other.content:
+				match=True
+				for k in range(len(sid)):
+					match=match and ( i[sid[k]]== j[oid[k]])
+						
+				if match:
+					item=list(i)
+					for l in noid:
+						item.append(j[l])
+					
+					newt.content.append(item)
+		
+		return newt
 		
 	def __str__(self):
 		'''Returns a string representation of the relation, can be printed with 

samples/skills.tlb

@@ -0,0 +1,17 @@
+id skill
+0 C
+0 Python
+1 Python
+1 C++
+1 SystemAdmin
+2 C
+2 PHP
+3 C++
+4 C++
+4 C
+4 Pearl
+5 Pearl
+5 C
+7 Python
+7 C
+7 PHP