Question

If a column is made unique in a database table structure, is there any need to do a check to see if a new value to be inserted already exists in the table via script? Or would it be fine just to insert values letting the DBMS filter non-new values?

Answer 1

You should always validate your data before inserting it on the database. That being said, what will happen if you try to insert a non-unique value on a unique defined column is an SQLexception.

In order to validate this before insertion, you could for example do a

 select 1
 from mytable_with_unique_column
 where my_unique_column = myNewValue

If the query returns anything, then simply do not try to insert as that will throw an SQLException.