单项选择题
You need to change the definition of an existing table. The COMMERCIALS table needs its DESCRIPTION column changed to hold varying length characters up to 1000 bytes. The column can currently hold 500 bytes per value. The table contains 20000 rows. Which statement is valid?（）
A.ALTER TABLE commercials MODIFY (description CHAR2(1000));
B.ALTER TABLE commercials CHANGE (description CHAR2(1000));
C.ALTER TABLE commercials CHANGE (description VARCHAR2(1000));
D.ALTER TABLE commercials MODIFY (description VARCHAR2(1000));
E.You cannot increase the size of a column if the table has rows.
相关考题
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单项选择题
You need to modify the STUDENTS table to add a primary key on the STUDENT_ID column. The table is currently empty. Which statement accomplishes this task?（）
A.ALTER TABLE students ADD PRIMARY KEY student_id;
B.ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id);
C.ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id;
D.ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);
E.ALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id); -
多项选择题
Which two statements about subqueries are true? （）
A.A subquery should retrieve only one row.
B.A subquery can retrieve zero or more rows.
C.A subquery can be used only in SQL query statements.
D.Subqueries CANNOT be nested by more than two levels.
E.A subquery CANNOT be used in an SQL query statement that uses group functions.
F.When 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. -
单项选择题
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 UPDATE statement is valid?（）
A.UPDATEnew_employeesSETname=（SELECTlast_nameFirst_nameFROMemployeesWHEREemployee_id=180）WHEREemployee_id=180；
B.UPDATEnew_employeesSETname=（SELECTlast_nameFirst_nameFROMemployees）WHEREemployee_id=180；
C.UPDATEnew_employeesSETname=（SELECTlast_nameFirst_nameFROMemployeesWHEREemployee_id=180） WHEREemployee_id=（SELECTemployee_idFROMnew_employees）；
D.UPDATEnew_employeesSETname=（SELECTlast_nameFirst_nameFROMemployeesWHEREemployee_id=（SELECTemployee_idFROMnew_employees） WHEREemployee_id=180；
