Add unique constraint depending on value in SQL

Question

i have a situation where i want to add unique constaint only when there is a certain value in other field for example the table is ID CategoryName Name Value CategoryID

Answer 1

One way to achieve this would be to have two tables, one for categoryId 0 and one for the rest. You can define the uniqueness constraint on the first table, and use a view and union any time you want to use them as a single table.

Answer 2

CREATE UNIQUE NONCLUSTERED INDEX [UQ_ID_CategoryName_Name, CategoryName, Name] ON TableName 
(
    ID, CategoryName, Name
)
WHERE (CategoryID = 0)

Answer 3

Create a filtered unique index on Name for CategoryID = 0.