How can I prevent inserting duplicate data into a SQL Server table?

Question

I have a series of data that need to be written into SQL, what should I do to check the data in SQL to prevent same data inserted into table?

Example data to be inse

Answer 1

If you do not want duplicate data, you should consider enforcing that at the DB level with a UNIQUE CONSTRAINT or a UNIQUE INDEX

SQL Server 2008 also has a MERGE statement you could use to check for matched records. This could be helpful if you want to update an existing record.