資料，資料，命根就在資料 ! 操作資料庫時，一定要謹慎小心。師萬物 這裡的程式碼看看就好，要有自己的判斷。遇到抉擇，要不恥上下問。

example

stu@Ubuntu:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 53
Server version: 8.0.12 MySQL Community Server - GPL

Copyright (c) 2000, 2018, Oracle and/or
 
 its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use db_chinese_medicine;
Reading table
 
 information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> select * from t_fruit;
+----+-----------+-------+--------+----------+------------------------------------+---------------------+---------------------+
| id |
 
 name      | count | price  | is_sales | note                               | gmt_create          | gmt_modified        |
+----+-----------+-------+--------+----------+------------------------------------+---------------------+---------------------+
|  1 | 甜瓜      |    10 |  3.210 |        1 | 無                                 | 2018-10-27 19:42:56 | 2018-10-27 19:42:56 |
|  2 | 烏梅      |    20 |  5.430 |        1 | 無                                 | 2018-10-27 19:46:21 | 2018-10-27 19:46:21 |
|  3 | 櫻桃      |    30 |  6.540 |        1 | 無                                 | 2018-10-27 19:46:48 | 2018-10-27 19:46:48 |
|  4 | 甘蔗      |    50 |  7.650 |        0 | 無                                 | 2018-10-27 19:51:13 | 2018-10-27 19:51:13 |
|  5 | 菠蘿蜜    |    50 |  8.760 |        1 | 菠蘿蜜和菠蘿是什麼關係?            | 2018-10-27 19:55:44 | 2018-10-27 19:55:44 |
|  6 | 無花果    |   100 |  8.760 |        1 | 無                                 | 2018-10-27 19:57:48 | 2018-10-27 19:57:48 |
|  7 | 山葡萄    |   200 |  5.550 |        1 | 無                                 | 2018-10-27 20:11:07 | 2018-10-27 20:11:07 |
|  8 | 無漏子    |     5 |  3.320 |        0 | 無                                 | 2018-10-27 20:11:07 | 2018-10-27 20:11:07 |
|  9 | 五斂子    |    12 |  6.010 |        0 | 無                                 | 2018-10-27 20:11:07 | 2018-10-27 20:11:07 |
| 10 | 藕        |    80 | 10.200 |        0 | 無                                 | 2018-10-27 20:11:07 | 2018-10-27 20:11:07 |
| 11 | 慄        |     5 |  3.320 |        0 | NULL                               | 2018-10-27 20:24:01 | 2018-10-27 20:24:01 |
| 12 | 龍眼      |    49 |  6.540 |        0 | NULL                               | 2018-10-27 20:24:01 | 2018-10-27 20:24:01 |
| 13 | 楂子      |     0 |  8.100 |        0 | NULL                               | 2018-10-27 20:24:01 | 2018-10-27 20:24:01 |
+----+-----------+-------+--------+----------+------------------------------------+---------------------+---------------------+
13 rows in set (0.00 sec)

mysql> select * from t_fruit where not(note = '無');
+----+-----------+-------+-------+----------+------------------------------------+---------------------+---------------------+
| id | name      | count | price | is_sales | note                               | gmt_create          | gmt_modified        |
+----+-----------+-------+-------+----------+------------------------------------+---------------------+---------------------+
|  5 | 菠蘿蜜    |    50 | 8.760 |        1 | 菠蘿蜜和菠蘿是什麼關係?            | 2018-10-27 19:55:44 | 2018-10-27 19:55:44 |
+----+-----------+-------+-------+----------+------------------------------------+---------------------+---------------------+
1 row in set (0.00 sec)

mysql> exit
Bye
stu@Ubuntu:~$ 

more knowledge

• 注意：在note列中有三種資料：無，null，普通評論。
• where not(note = ‘無’) 語句不但忽略了 無，而且還把 null 也給忽略了！

resource

MySQL是一個關係型資料庫管理系統，目前是開源的(2018-10)。 許可權明確，恰當選擇引擎與字符集，命名簡潔明瞭與規範。 MariaDB，Redis，MongoDB，PostgreSQL，Hive，HBase等，可以簡單地瞭解。 Workbench，phpMyAdmin，Navicat等圖形化管理工具，可以試用一下。