A.NULL values are treated as zero.

B.NULL values represent missing or unknown data.

C.NULL values are not allowed in relational databases.

D.NULL values are treated as empty strings.

A.Combines rows from two queries and includes all duplicates

B.Returns rows from the first query that are not present in the second query

C.Returns rows that are present in both queries

D.Combines all rows from two queries without any conditions

A.To delete duplicate rows from a table

B.To update existing rows or insert new rows in a target table

C.To join two tables into one

D.To combine the results of two queries

A.To restart a transaction

B.To set a point within a transaction to which a rollback can occur

C.To save changes permanently

D.To delete data temporarily

A.If the subquery references the outer query

B.If the subquery returns any rows

C.If the subquery returns a specific number of rows

D.If the subquery contains only unique values