Trying to add FK_constraints but could not understand what happened?

Question

ALTER TABLE [PartyAddressHistory] ADD CONSTRAINT [FK_PartyAddressHistory_Address] FOREIGN KEY(AddressID)REFERENCES [Address](AddressID)----N
sg 547, Level 16, State 0, Line 1
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_PartyAddressHistory_Address". The conflict occurred in database "test1MDM", table "dbo.Address", column 'AddressID'.
ALTER TABLE [PartyAddress] ADD CONSTRAINT [FK_PartyAddress_Address] FOREIGN KEY(AddressID)REFERENCES [Address](AddressID)----N
Msg 547, Level 16, State 0, Line 1
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_PartyAddress_Address". The conflict occurred in database "test1MDM", table "dbo.Address", column 'AddressID'.
ALTER TABLE [PartySport] ADD CONSTRAINT [FK_PartySport_Leagues] FOREIGN KEY(LeagueID)REFERENCES [Leagues](LeagueID)----N
Msg 547, Level 16, State 0, Line 1
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_PartySport_Leagues". The conflict occurred in database "test1MDM", table "dbo.Leagues", column 'LeagueID'.

Answer 1

Well, the error is actually clear. It means that PartyAddressHistory table has values in the AddressID column which are not in the Address table.
You have the same problem in the PartyAddress table and PartySport has a similar problem.
To find bad rows try
select * from PartyAddress PA where not exists (select 1 from Address A where A.AddressID = PA.AddressID) -- similar statements for other tables.
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