Question 11 :
Indexes can usually be created for both primary and secondary keys.
Question 12 :
Each index consumes extra storage space and also requires overhead maintenance time whenever indexed data change value.
Question 13 :
The HAVING clause acts like a WHERE clause, but it identifies groups that meet a criterion, rather than rows.
Question 14 :
SQL is a data sublanguage.
Question 15 :
The qualifier DISTINCT must be used in an SQL statement when we want to eliminate duplicate rows.