QUESTION NO: 8

Where can subqueries be used? (Choose all that apply)

A. field names in the SELECT statement

B. the FROM clause in the SELECT statement

C. the HAVING clause in the SELECT statement

D. the GROUP BY clause in the SELECT statement

E. the WHERE clause in only the SELECT statement

F. the WHERE clause in SELECT as well as all DML statements

Answer: A,B,C,F

答案解析：

Explanation:

SUBQUERIES can be used in the SELECT list and in the FROM, WHERE, and HAVING clauses of a query.

A subquery can have any of the usual clauses for selection and projection. The following are required clauses:

A SELECT list

A FROM clause

The following are optional clauses:

WHERE

GROUP BY

HAVING

The subquery (or subqueries) within a statement must be executed before the parent query that calls it, in order that the results of the subquery can be passed to the parent.