在卧式铣床上,安装在主轴套中间和后端的是向心推力圆锥滚子轴承,这种轴承的特点是能够承受较大的轴向载荷。而且在承受轴向载荷较大的工作状态下,所允许的转速仅比向心推力球轴承低一些,但要比推力球轴承高得多。合适的()能限制轴承的发热,保持轴承的精度和提高轴承的工作寿命。
A. 转速
B. 预紧力
C. 径向力
D. 轴向力
The EMPLOYEES table contains these columns: LAST_NAME VARCHAR2 (25) SALARY NUMBER (6,2) COMMISSION_PCT NUMBER (6) You need to write a query that will produce these results: 1. Display the salary multiplied by the commission_pct. 2. Exclude employees with a zero commission_pct. 3. Display a zero for employees with a null commission value. Evaluate the SQL statement: SELECT LAST_NAME, SALARY*COMMISSION_PCT FROM EMPLOYEES WHERE COMMISSION_PCT IS NOT NULL; What does the statement provide? ()
All of the desired results
B. Two of the desired results
C. One of the desired results
D. An error statement