搜搜做题作业网Oracle 中 using的用法问题
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Oracle 中 using的用法问题
1.
SELECT e.last_name,d.department_name,d.location_id
FROM employees e JOIN departments d
USING (department_id );
里面using （department_id
2Q:In which three cases would you use the USING clause?(Choose three.)
A.You want to create a nonequijoin.
B.The tables to be joined have multiple NULL columns.
C.The tables to be joined have columns of the same name and different data types.
D.The tables to be joined have columns with the same name and compatible data types.
E.You want to use a NATURAL join,but you want to restrict the number of columns in the join condition.
能举例说明下吗?
1.
SELECT e.last_name,d.department_name,d.location_id
FROM employees e JOIN departments d
USING (department_id );
里面using （department_id
2Q:In which three cases would you use the USING clause?(Choose three.)
A.You want to create a nonequijoin.
B.The tables to be joined have multiple NULL columns.
C.The tables to be joined have columns of the same name and different data types.
D.The tables to be joined have columns with the same name and compatible data types.
E.You want to use a NATURAL join,but you want to restrict the number of columns in the join condition.
能举例说明下吗?
1.相当于 on e.department_id = d.department_id
即通过该字段将两个表关连
2.BDE
即通过该字段将两个表关连
2.BDE