C＃标志枚举的SQL Server唯一约束

Question

Let's say I have the following columns:

Name | Address| Type

The Type is stored as an int in SQL Server and corresponds to a C# flag enum. I want to declare a unique constraint across the name, Address and type columns such that for a particular name and address, two entries do not have the same flags. For example the following two entries will be legal:

John | NY | 1  
John | NY | 2 

but these two will not (since the first bit is 1 for both):

Jane | NY | 1  
Jane | NY | 3 

Is there a simple way to implement this? Thanks!

Answer 1

You are approaching this the wrong way.

Don't stuff the flags into integer columns! If you really want, you can store them as bit , but tinyint is often fine:

Type1 bit,
Type2 bit,
. . .

Then create unique indexes:

 create unique index t_name_address_type1 on t(name, address, type1);
 create unique index t_name_address_type2 on t(name, address, type2);
 . . . 

If, for some reason, you have to store multiple values in an integer column, then you can create separate flag columns using computed columns:

alter table t add type1 as (case when intcol & 1 > 0 then 1 else 0 end);
alter table t add type2 as (case when intcol & 2 > 0 then 1 else 0 end);
. . .

Then you can create the unique indexes on the computed columns.