sql server 2008 - SQL table design with contigent constraints -

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i have table design problem need cunning solution.

let's have 2 tables, relationship:

contract 1---n payment

now, let's have legacy data needs go these tables. problem though many of legacy payment entries aggregated across mulitple contracts

so view as:

new:

somethingabovecontract 1---n contract 1---n payment

legacy:

somethingabovecontract 1---n payment

now, can around creating m-n relationship between contract , payment. 

contract 1---n contractpayment n---1 payment

(it possible me identify contracts linked aggregated payment)

this fine legacy data, want enforce 1-n relationship between contract , payment going forward. so, using unhandy scribble illustrate, this:

enter image description here

i.e. payment aggregate, contractid null, otherwise should not null. in other words, need find way enforce following contingencies on payment table:

  1. contractid nullable if paymentid appears in contractpayment
  2. contractid not nullable if paymentid not appear in contractpayment

i don't know how though.

even if possible, seem bit ugly (which legacy data conversion invariably is). if has more elegant solution great. otherwise, works!

thanks
karl

use 2 (sets of) tables, 1 'legacy' , 1 going forward. should able define business rules , without need nullable columns (sql's 3 value logic disaster). privileges revoked on 'legacy' table(s) ensure not used going forward.


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