Обсуждение: Column References
I've got a question about references, is it possible to specify criteria for the Reference. For example, Table 1 has Field1 That References Field1 in Table2, However I only want Field 1 in Table 1 to reference the Records in Table2 that have the Valid Field set to TRUE. In other words, I don't want the user to be able to enter invalid records from table 2 into field 1 in table 1. Is there a different way of accomplishing the same thing?
On Fri, Oct 31, 2003 at 13:44:40 -0600, "Epps, Aaron M." <Epps.Aaron@mayo.edu> wrote: > I've got a question about references, is it possible to specify criteria for the Reference. For example, Table 1 hasField1 That References Field1 in Table2, However I only want Field 1 in Table 1 to reference the Records in Table2 thathave the Valid Field set to TRUE. In other words, I don't want the user to be able to enter invalid records from table2 into field 1 in table 1. Is there a different way of accomplishing the same thing? The way I have done this is to use redundant data in table1. For example in your case you might include a Valid field in table 1 with a constraint forcing it to always be true. Then you can use a two column foreign key reference from table 1 to table 2 that will enforce your constraint. (You will also need to make a unique index on the two column combination in table2.)