1Z0-051 QUESTION 7 ON和USING的用法

QUESTION 7

Which two statements are true regarding the USING and ON clauses in table joins? (Choose two.)
A. Both USING and ON clauses can be used for equijoins and nonequijoins.
B. A maximum of one pair of columns can be joined between two tables using the ON clause.
C. The ON clause can be used to join tables on columns that have different names but compatible data
types.
D. The WHERE clause can be used to apply additional conditions in SELECT statements containing the

ON or the USING clause.

答案是CD。

解析：

根据ORACLE官方文档：

http://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_10002.htm#SQLRF55312

ON condition Use the ON clause to specify a join condition. Doing so lets you specify join conditions separate from any search or filter conditions in the WHEREclause.

USING (column) When you are specifying an equijoin of columns that have the same name in both tables, the USING column clause indicates the columns to be used. You can use this clause only if the join columns in both tables have the same name. Within this clause, do not qualify the column name with a table name or table alias.

对于A选项，USING只能用在equijion，因此错误。

对于B选项，ON可以执行多行连接。

C选项和D选项都正确。