对视图进行增删改查，会影响到原表数据。
    对原表进行增删改查，会影响到视图数据。
    视图可以隐藏表的实现细节，保密级别较高的系统，数据库只对外提供相关的视图。

    1. mysql> create view emp_view as select * from emp;
    2. Query OK, 0 rows affected (0.03 sec)
    4. mysql> select * from emp_view;
    5. +-------+--------+-----------+------+------------+---------+---------+--------+
    6. | EMPNO | ename  | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
    7. +-------+--------+-----------+------+------------+---------+---------+--------+
    8. |  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 | NULL    |     20 |
    9. |  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
    10. |  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
    11. |  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 | NULL    |     20 |
    12. |  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
    13. |  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 | NULL    |     30 |
    14. |  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 | NULL    |     10 |
    15. |  7788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 | 3000.00 | NULL    |     20 |
    16. |  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL    |     10 |
    17. |  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
    18. |  7876 | ADAMS  | CLERK     | 7788 | 1987-05-23 | 1100.00 | NULL    |     20 |
    19. |  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 | NULL    |     30 |
    20. |  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 | NULL    |     20 |
    21. |  7934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 | NULL    |     10 |
    22. +-------+--------+-----------+------+------------+---------+---------+--------+
    23. 14 rows in set (0.08 sec)
    25. mysql> update emp_view set ename = 'zhangsan' where empno = 7369;
    26. Query OK, 1 row affected (0.02 sec)
    27. Rows matched: 1  Changed: 1  Warnings: 0
    29. mysql> select * from emp_view;
    30. +-------+----------+-----------+------+------------+---------+---------+--------+
    31. | EMPNO | ename    | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
    32. +-------+----------+-----------+------+------------+---------+---------+--------+
    33. |  7369 | zhangsan | CLERK     | 7902 | 1980-12-17 |  800.00 | NULL    |     20 |
    34. |  7499 | ALLEN    | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
    35. |  7521 | WARD     | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
    36. |  7566 | JONES    | MANAGER   | 7839 | 1981-04-02 | 2975.00 | NULL    |     20 |
    37. |  7654 | MARTIN   | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
    38. |  7698 | BLAKE    | MANAGER   | 7839 | 1981-05-01 | 2850.00 | NULL    |     30 |
    39. |  7782 | CLARK    | MANAGER   | 7839 | 1981-06-09 | 2450.00 | NULL    |     10 |
    40. |  7788 | SCOTT    | ANALYST   | 7566 | 1987-04-19 | 3000.00 | NULL    |     20 |
    41. |  7839 | KING     | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL    |     10 |
    42. |  7844 | TURNER   | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
    43. |  7876 | ADAMS    | CLERK     | 7788 | 1987-05-23 | 1100.00 | NULL    |     20 |
    44. |  7900 | JAMES    | CLERK     | 7698 | 1981-12-03 |  950.00 | NULL    |     30 |
    45. |  7902 | FORD     | ANALYST   | 7566 | 1981-12-03 | 3000.00 | NULL    |     20 |
    46. |  7934 | MILLER   | CLERK     | 7782 | 1982-01-23 | 1300.00 | NULL    |     10 |
    47. +-------+----------+-----------+------+------------+---------+---------+--------+
    48. 14 rows in set (0.07 sec)
    50. mysql> select * from emp;
    51. +-------+----------+-----------+------+------------+---------+---------+--------+
    52. | EMPNO | ename    | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
    53. +-------+----------+-----------+------+------------+---------+---------+--------+
    54. |  7369 | zhangsan | CLERK     | 7902 | 1980-12-17 |  800.00 | NULL    |     20 |
    55. |  7499 | ALLEN    | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
    56. |  7521 | WARD     | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
    57. |  7566 | JONES    | MANAGER   | 7839 | 1981-04-02 | 2975.00 | NULL    |     20 |
    58. |  7654 | MARTIN   | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
    59. |  7698 | BLAKE    | MANAGER   | 7839 | 1981-05-01 | 2850.00 | NULL    |     30 |
    60. |  7782 | CLARK    | MANAGER   | 7839 | 1981-06-09 | 2450.00 | NULL    |     10 |
    61. |  7788 | SCOTT    | ANALYST   | 7566 | 1987-04-19 | 3000.00 | NULL    |     20 |
    62. |  7839 | KING     | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL    |     10 |
    63. |  7844 | TURNER   | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
    64. |  7876 | ADAMS    | CLERK     | 7788 | 1987-05-23 | 1100.00 | NULL    |     20 |
    65. |  7900 | JAMES    | CLERK     | 7698 | 1981-12-03 |  950.00 | NULL    |     30 |
    66. |  7902 | FORD     | ANALYST   | 7566 | 1981-12-03 | 3000.00 | NULL    |     20 |
    67. |  7934 | MILLER   | CLERK     | 7782 | 1982-01-23 | 1300.00 | NULL    |     10 |
    68. +-------+----------+-----------+------+------------+---------+---------+--------+
    69. 14 rows in set (0.07 sec)
    71. mysql> delete from emp_view where empno = 7499;
    72. Query OK, 1 row affected (0.01 sec)
    74. mysql> select * from emp_view;
    75. +-------+----------+-----------+------+------------+---------+---------+--------+
    76. | EMPNO | ename    | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
    77. +-------+----------+-----------+------+------------+---------+---------+--------+
    78. |  7369 | zhangsan | CLERK     | 7902 | 1980-12-17 |  800.00 | NULL    |     20 |
    79. |  7521 | WARD     | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
    80. |  7566 | JONES    | MANAGER   | 7839 | 1981-04-02 | 2975.00 | NULL    |     20 |
    81. |  7654 | MARTIN   | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
    82. |  7698 | BLAKE    | MANAGER   | 7839 | 1981-05-01 | 2850.00 | NULL    |     30 |
    83. |  7782 | CLARK    | MANAGER   | 7839 | 1981-06-09 | 2450.00 | NULL    |     10 |
    84. |  7788 | SCOTT    | ANALYST   | 7566 | 1987-04-19 | 3000.00 | NULL    |     20 |
    85. |  7839 | KING     | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL    |     10 |
    86. |  7844 | TURNER   | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
    87. |  7876 | ADAMS    | CLERK     | 7788 | 1987-05-23 | 1100.00 | NULL    |     20 |
    88. |  7900 | JAMES    | CLERK     | 7698 | 1981-12-03 |  950.00 | NULL    |     30 |
    89. |  7902 | FORD     | ANALYST   | 7566 | 1981-12-03 | 3000.00 | NULL    |     20 |
    90. |  7934 | MILLER   | CLERK     | 7782 | 1982-01-23 | 1300.00 | NULL    |     10 |
    91. +-------+----------+-----------+------+------------+---------+---------+--------+
    92. 13 rows in set (0.07 sec)
    94. mysql> select * from emp;
    95. +-------+----------+-----------+------+------------+---------+---------+--------+
    96. | EMPNO | ename    | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
    97. +-------+----------+-----------+------+------------+---------+---------+--------+
    98. |  7369 | zhangsan | CLERK     | 7902 | 1980-12-17 |  800.00 | NULL    |     20 |
    99. |  7521 | WARD     | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
    100. |  7566 | JONES    | MANAGER   | 7839 | 1981-04-02 | 2975.00 | NULL    |     20 |
    101. |  7654 | MARTIN   | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
    102. |  7698 | BLAKE    | MANAGER   | 7839 | 1981-05-01 | 2850.00 | NULL    |     30 |
    103. |  7782 | CLARK    | MANAGER   | 7839 | 1981-06-09 | 2450.00 | NULL    |     10 |
    104. |  7788 | SCOTT    | ANALYST   | 7566 | 1987-04-19 | 3000.00 | NULL    |     20 |
    105. |  7839 | KING     | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL    |     10 |
    106. |  7844 | TURNER   | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
    107. |  7876 | ADAMS    | CLERK     | 7788 | 1987-05-23 | 1100.00 | NULL    |     20 |
    108. |  7900 | JAMES    | CLERK     | 7698 | 1981-12-03 |  950.00 | NULL    |     30 |
    109. |  7902 | FORD     | ANALYST   | 7566 | 1981-12-03 | 3000.00 | NULL    |     20 |
    110. |  7934 | MILLER   | CLERK     | 7782 | 1982-01-23 | 1300.00 | NULL    |     10 |
    111. +-------+----------+-----------+------+------------+---------+---------+--------+
    112. 13 rows in set (0.07 sec)
    114. mysql> update emp set ename = 'li' where empno = 7521;
    115. Query OK, 1 row affected (0.01 sec)
    116. Rows matched: 1  Changed: 1  Warnings: 0
    118. mysql> select * from emp;
    119. +-------+----------+-----------+------+------------+---------+---------+--------+
    120. | EMPNO | ename    | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
    121. +-------+----------+-----------+------+------------+---------+---------+--------+
    122. |  7369 | zhangsan | CLERK     | 7902 | 1980-12-17 |  800.00 | NULL    |     20 |
    123. |  7521 | li       | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
    124. |  7566 | JONES    | MANAGER   | 7839 | 1981-04-02 | 2975.00 | NULL    |     20 |
    125. |  7654 | MARTIN   | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
    126. |  7698 | BLAKE    | MANAGER   | 7839 | 1981-05-01 | 2850.00 | NULL    |     30 |
    127. |  7782 | CLARK    | MANAGER   | 7839 | 1981-06-09 | 2450.00 | NULL    |     10 |
    128. |  7788 | SCOTT    | ANALYST   | 7566 | 1987-04-19 | 3000.00 | NULL    |     20 |
    129. |  7839 | KING     | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL    |     10 |
    130. |  7844 | TURNER   | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
    131. |  7876 | ADAMS    | CLERK     | 7788 | 1987-05-23 | 1100.00 | NULL    |     20 |
    132. |  7900 | JAMES    | CLERK     | 7698 | 1981-12-03 |  950.00 | NULL    |     30 |
    133. |  7902 | FORD     | ANALYST   | 7566 | 1981-12-03 | 3000.00 | NULL    |     20 |
    134. |  7934 | MILLER   | CLERK     | 7782 | 1982-01-23 | 1300.00 | NULL    |     10 |
    135. +-------+----------+-----------+------+------------+---------+---------+--------+
    136. 13 rows in set (0.08 sec)
    138. mysql> select * from emp_view;
    139. +-------+----------+-----------+------+------------+---------+---------+--------+
    140. | EMPNO | ename    | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
    141. +-------+----------+-----------+------+------------+---------+---------+--------+
    142. |  7369 | zhangsan | CLERK     | 7902 | 1980-12-17 |  800.00 | NULL    |     20 |
    143. |  7521 | li       | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
    144. |  7566 | JONES    | MANAGER   | 7839 | 1981-04-02 | 2975.00 | NULL    |     20 |
    145. |  7654 | MARTIN   | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
    146. |  7698 | BLAKE    | MANAGER   | 7839 | 1981-05-01 | 2850.00 | NULL    |     30 |
    147. |  7782 | CLARK    | MANAGER   | 7839 | 1981-06-09 | 2450.00 | NULL    |     10 |
    148. |  7788 | SCOTT    | ANALYST   | 7566 | 1987-04-19 | 3000.00 | NULL    |     20 |
    149. |  7839 | KING     | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL    |     10 |
    150. |  7844 | TURNER   | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
    151. |  7876 | ADAMS    | CLERK     | 7788 | 1987-05-23 | 1100.00 | NULL    |     20 |
    152. |  7900 | JAMES    | CLERK     | 7698 | 1981-12-03 |  950.00 | NULL    |     30 |
    153. |  7902 | FORD     | ANALYST   | 7566 | 1981-12-03 | 3000.00 | NULL    |     20 |
    154. |  7934 | MILLER   | CLERK     | 7782 | 1982-01-23 | 1300.00 | NULL    |     10 |
    155. +-------+----------+-----------+------+------------+---------+---------+--------+
    156. 13 rows in set (0.08 sec)