多项选择题
Which two statements about sequences are true? （）
A. You use a NEXTVAL pseudo column to look at the next possible value that would be generated from a sequence, without actually retrieving the value.
B. You use a CURRVAL pseudo column to look at the current value just generated from a sequence, without affecting the further values to be generated from the sequence.
C. You use a NEXTVAL pseudo column to obtain the next possible value from a sequence by actually retrieving the value from the sequence.
D. You use a CURRVAL pseudo column to generate a value from a sequence that would be used for a specified database column.
E. If a sequence starting from a value 100 and incremented by 1 is used by more then one application, then all of these applications could have a value of 105 assigned to their column whose value is being generated by the sequence.
F. You use REUSE clause when creating a sequence to restart the sequence once it generates the maximum value defined for the sequence.
相关考题
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单项选择题
Examine the structure of the EMPLOYEES table: EMPLOYEE_ID NUMBER NOT NULL EMP_NAME VARCHAR2(30) JOB_ID VARCHAR2(20) DEFAULT SA_REP SAL NUMBER COMM_PCT NUMBER MGR_ID NUMBER DEPARTMENT_ID NUMBER You need to update the records of employees 103 and 115. The UPDATE statement you specify should update the rows with the values specified below: JOB_ID: Default value specified for this column definition. SAL: Maximum salary earned for the job ID SA_REP. COMM_PCT: Default value specified for this commission percentage column, if any. If no default value is specified for the column, the value should be NULL. DEPARTMENT_ID: Supplied by the user during run time through substitution variable. Which UPDATE statement meets the requirements?（）
A. UPDATE employees SET job_id = DEFAULT AND Sal = (SELECT MAX(sal) FROM employees WHERE job_id = 'SA_REP') AND comm_pct = DEFAULT AND department_id = &did WHERE employee _id IN (103,115);
B. UPDATE employees SET job_id = DEFAULT AND Sal = MAX(sal) AND comm_pct = DEFAULT OR NULL AND department_id = &did WHERE employee_id IN (103,115) AND job _ id = 'SA_ REP';
C. UPDATE employees SET job_id = DEFAULT, Sal = (SELECT MAX(sal) FROM employees WHERE job_id = 'SA_REP'), comm_pct = DEFAULT, department_id = &did WHERE employee_id IN (103,115);
D. UPDATE employees SET job_id = DEFAULT, Sal = MAX(sal), comm_pct = DEFAULT, department_id = &did WHERE employee_id IN (103,115) AND job _ id = 'SA_ REP';
E. UPDATE employees SET job_id = DEFAULT, Sal = (SELECT MAX(sal) FROM employees WHERE job_id = 'SA_REP') comm_pct = DEFAULT OR NULL, department_id = &did WHERE employee_id IN (103,115); -
多项选择题
Which three statements about subqueries are true?（）
A. A single row subquery can retrieve only one column and one row.
B. A single row subquery can retrieve only one row but many columns.
C. A multiple row subquery can retrieve multiple rows and multiple columns.
D. A multiple row subquery can be compared by using the ">" operator.
E. A single row subquery can use the IN operator.
F. A multiple row subquery can use the "=" operator. -
单项选择题
In a SELECT statement that includes a WHERE clause, where is the GROUP BY clause placed in the SELECT statement?（）
A. Immediately after the SELECT clause
B. Before the WHERE clause
C. Before the FROM clause
D. After the ORDER BY clause
E. After the WHERE clause
