我不清楚您打算如何使用带有fk约束的表，但看起来您很可能可以用更好的方式设计数据库。也就是说，您可以在生成的列上使用约束来实现这一点：

create table customers_payment_method (
customer_id int not null,
payment_method varbinary(8),
customer_id_cashapp int as
  (case payment_method when 'cashapp' then customer_id end) stored,
customer_id_paypal int as
  (case payment_method when 'paypal' then customer_id end) stored,
constraint cidcashapp foreign key (customer_id_cashapp) references customers_cashapp(customer_id),
constraint cidpaypal foreign key (customer_id_paypal) references customers_paypal(customer_id)
);

fiddle