Question : Implementing an Entiity Relation diagram

I am a student database designer.  I'm trying to link these two tables below: CONTRACT and PRICEPLAN

I want the two tables to be linked together via the 'PlanCode' field.  

The CONTRACT table details customer data and specifies what "plancode" they have.

The PRICEPLAN table details cost information for telephone services

When I try to implement the PRICEPLAN table in Oracle and put 'plancode' as a foreign key for CONTRACT, it says 'no matching unique or primary key for this column-list'

Any suggestions on how I can implement this?


CONTRACT      
Account#      Phone#      ContractDate      PlanCode
12345      746-5487      2/2/1990      ABC
12346      548-5486      25/2/91      ABC
12347      246-8754      1/4/1988      BCD
12348      587-5487      14/3/89      BCD
12349      364-2154      21/4/94      ABC

PRICEPLAN      
PlanCode      ServiceType      Cost
ABC      VoiceCallPk      5
ABC      DataCallPk      4
ABC      MMCallPk      7
ABC      TextMsgPk      2
ABC      MMMsgPk      3
ABC      VoiceCall      4
ABC      DataCall      3
ABC      MMCall      6
ABC      TextMsg      1
ABC      MMMsg      2
BCD      VoiceCallPk      6
BCD      DataCallPk      5
BCD      MMCallPk      8
BCD      TextMsgPk      3
BCD      MMMsgPk      4
BCD      VoiceCall      5
BCD      DataCall      4
BCD      MMCall      7
BCD      TextMsg      2
BCD      MMMsg      3

Answer : Implementing an Entiity Relation diagram

>> 'plancode' as a foreign key for CONTRACT
Foreign keys require the master table column to be UNIQUE/ a primary key column.
Here plancode in CONTRACT is none of them.
You cannot implement this constraint here.

Alternative is: You can have another table for placodes. ANd have a foreign key constraint to that table from CONTRACT and PRICEPLAN.