所謂 CRUD => Create , Read , Update , Delete 指的就是增刪改查，為資料庫一個很重要的地方。
前面我們做過C CREATE,R SELECT了，接下來要來操輟關於UPDATE、DELETE的部分。

UPDATE table_name set ...:UPDATE能夠修改我們現有的資料。

透過,可以一次改變多個column。

UPDATE table_name set salary=8700,notes=updated where title="Software Engineer"

+----+------------+-----------+-------------------+--------+------------+-------+

| id | first_name | last_name | title             | salary | hire_date  | notes |

+----+------------+-----------+-------------------+--------+------------+-------+

|  1 | Robin      | Jackman   | Software Engineer |   8700 | 2001-10-12 | updated  |

|  5 | Eliza      | Clifford  | Software Engineer |   8700 | 1998-10-19 | updated  |

|  6 | Nancy      | Newman    | Software Engineer |   8700 | 2007-01-23 | updated  |

+----+------------+-----------+-------------------+--------+------------+-------+

DELETE from table_name ...:刪除特定資料。

DELETE from  employee  where title="Software Engineer";
uery OK, 3 rows affected (0.01 sec)

可發現其資料已經消失。
mysql> SELECT * from employee;
+----+------------+-----------+------------------------+--------+------------+-------+
| id | first_name | last_name | title                  | salary | hire_date  | notes |
+----+------------+-----------+------------------------+--------+------------+-------+
|  2 | Taylor     | Edward    | Software Architect     |   7200 | 2002-09-21 | NULL  |
|  3 | Vivian     | Dickens   | Database Administrator |   6000 | 2012-08-29 | NULL  |
|  4 | Harry      | Clifford  | Database Administrator |   6800 | 2015-12-10 | NULL  |
|  7 | Melinda    | Clifford  | Project Manager        |   8500 | 2013-10-29 | NULL  |
|  8 | Jack       | Chan      | Test Engineer          |   6500 | 2018-09-07 | NULL  |
|  9 | Harley     | Gilbert   | Software Architect     |   8000 | 2000-07-17 | NULL  |
+----+------------+-----------+------------------------+--------+------------+-------+
6 rows in set (0.00 sec)

DELETE from table_name 可以刪除指定之table所有的資料。

CREATE TABLE IF NOT EXISTS table_name:IF NOT EXISTS代表如果這個table不存在，我們就執行CREATE TABLE，反之。

原本我們不加上IF NOT EXISTS雖然還是有執行INSERT的部分，但還是會報錯，而加上以後，就沒有報錯INSERT的部分也有執行，整個代碼會更加嚴謹。