Can set unique constraint in table have data not unique SQL Server? I have a table with has many rows, I want to set unique constraint for this table, but the column that must be unique, has data is not unique. Is any way to set unique constraint for this table for this column or unique constraint for any insert or update next time?

I can't delete data because is real
You can use a filtered unique undex to apply a uniqueness constraint to a filtered set of data. For example this: http://sqlmag.com/blog/whats-good-use-unique-filtered-index

For example you could exclude your non unique rows from the index and make it unique

But you really need to fix your data or it's going to cause you problems in future.