A primary key constraint ensures that each value in the column or set of columns is unique and that no null values are allowed. This constraint is designed specifically to prevent duplicate values, making it the appropriate answer for ensuring that identical values are never stored in a set of columns in a table.
A COMMIT statement concludes the current transaction, making all changes made by UPDATE and DELETE commands permanent. Once the COMMIT is complete, a new unit of work is initiated, and it is not possible to undo the committed changes with a ROLLBACK command. Thus, the correct choice is that it finishes the current T1 unit of work and a new one is initiated, committing all changes made during T1.
There are three main types of stored procedures which can be deployed: SQL procedures, external procedures, and sourced procedures. SQL procedures are written using SQL and run within the database server. External procedures are written in an external programming language and linked to the database. Sourced procedures are based on an existing procedure. These distinctions cover the general categories of stored procedures in many relational database management systems.
DB2 Express Server Edition has been discontinued in version 11.1 of DB2 LUW. This information can be verified through IBM's official documentation, which explicitly states the discontinuation of the DB2 Express Server Edition in this version.