Add PK to Person_likes_Message edge table

Author: GLaDAP

mssql/ddl/schema-constraints.sql

@@ -4,6 +4,7 @@ ALTER TABLE Forum_hasMember_Person ADD PRIMARY KEY (ForumId, PersonId);
 ALTER TABLE Forum_hasTag_Tag ADD PRIMARY KEY (ForumId, TagId);
 ALTER TABLE Person_hasInterest_Tag ADD PRIMARY KEY (PersonId, TagId);
 ALTER TABLE Person_knows_Person ADD PRIMARY KEY (Person1Id, Person2Id);
+ALTER TABLE Person_likes_Message ADD PRIMARY KEY (PersonId, MessageId);
 ALTER TABLE Person_studyAt_University ADD PRIMARY KEY (PersonId, UniversityId);
 ALTER TABLE Person_workAt_Company ADD PRIMARY KEY (PersonId, CompanyId);
 ALTER TABLE Message_hasTag_Tag ADD PRIMARY KEY (MessageId, TagId);