Which type of union opposes the interests of employers

In paging, the page size is defined by:

In a relational database, what is a candidate key?

Multiversion Concurrency Control (MVCC) ensures:

What does re.sub(r'(\w+)', r'_\1_', 'hello world') return?

Given the following Python-like code snippet: 

   ```python

    class Counter:

        def __init__(self):

Which key uniquely identifies a record in a table?

Which operation is NOT part of relational algebra?

Which SQL isolation level allows phantom reads but prevents dirty reads and non-repeatable reads?

What will re.findall(r'\d+', 'abc123def45ghi') return? 

Which normal form eliminates transitive dependency?