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Examine the structure of the EMPLOYEES and NEW_EMPLOYEES tables: EMPLOYEES EMPLOYEE_ID NUMBER Primary Key FIRST_NAME VARCHAR2(25) LAST_NAME VARCHAR2(25) HIRE_DATE DATE NEW_EMPLOYEES EMPLOYEE_ID NUMBER Primary Key NAME VARCHAR2(60) Which DELETE statement is valid?()
A、DELETE FROM employees WHERE employee_id = (SELECT employee_id FROM employees);
B、DELETE * FROM employees WHERE employee_id = (SELECT employee_id FROM new_employees);
C、DELETE FROM employees WHERE employee_id IN (SELECT employee_id FROM new_employees WHERE name ='Carrey');
D、DELETE * FROM employees WHERE employee_id IN (SELECT employee_id FROM new_employees WHERE last_name ='Carrey');
以太网交换机和网桥工作在OSI模型的哪一层()。
A、数据链路层
B、传输层
C、网络层
D、会话层
Which two statements about subqueries are true? ()
AA subquery should retrieve only one row.
BA subquery can retrieve zero or more rows.
CA subquery can be used only in SQL query statements.
DSubqueries CANNOT be nested by more than two levels.
EA subquery CANNOT be used in an SQL query statement that uses group functions.
FWhen a subquery is used with an inequality comparison operator in the outer SQL statement, the column list in the SELECT clause of the subquery should contain only one column.
To determine the space allocated for temporary segments, the DBA can access which of the following views? ()
A、DBA_TABLESPACES
B、DBA_TABLES
C、DBA_SEGMENTS
D、DBA_FREE_SPACE
AutoCAD2008的图形文件和样板文件的扩展名分别是()。
A、dwg和bak
B、dwg和dwt
C、dwg和doc
D、doc和bmp