MariaDB – 常用處理資訊函數 ( Information Functions )

測試環境為 CentOS 8 x86_64 虛擬機.

1. 字串函數 ( String Functions ) 與 型別轉換 – https://benjr.tw/102953
2. 數字函數 (Numeric Functions) – https://benjr.tw/101970
3. 日期與時間函數 (Date & Time Functions) – https://benjr.tw/102964
4. 資訊函數 (Information Functions) – 這邊介紹.
5. 搭配 GROUP BY 函數 (Aggregate Functions) – https://benjr.tw/102967
6. 流程控制函數 (Control Flow Functions) – https://benjr.tw/102747

先建立一個測試用資料庫 (testdb) , 與 tables (employee) ,下面範例會使用到 . 格式為 K1 int(11) – auto_increment & PRIMARY KEY , Name char(20), Dept char(20), jobTitle char(20) ,email char(30) 以及 Salary int(11).

SELECT 查詢需注意資料庫字元編碼 Character Sets 與 文字排序 Collations ,請參考資料庫編碼 – https://benjr.tw/102156 .

[root@localhost ~]# mysql -u root -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 12
Server version: 10.3.11-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

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

MariaDB [(none)]> CREATE DATABASE testdb DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
Query OK, 1 row affected (0.001 sec)

MariaDB [(none)]> USE testdb;
Database changed
MariaDB [testdb]> CREATE TABLE employee (K1 int(11) NOT NULL auto_increment, Name char(20) NOT NULL, Dept char(20) NOT NULL, JobTitle char(20) NOT NULL, Salary int(11) NOT NULL , email char(30) NOT NULL, PRIMARY KEY (K1)) ;
Query OK, 0 rows affected (0.010 sec)
 
MariaDB [testdb]> DESCRIBE employee; 
+----------+----------+------+-----+---------+----------------+
| Field    | Type     | Null | Key | Default | Extra          |
+----------+----------+------+-----+---------+----------------+
| K1       | int(11)  | NO   | PRI | NULL    | auto_increment |
| Name     | char(20) | NO   |     | NULL    |                |
| Dept     | char(20) | NO   |     | NULL    |                |
| JobTitle | char(20) | NO   |     | NULL    |                |
| Salary   | int(11)  | NO   |     | NULL    |                |
| email    | char(30) | NO   |     | NULL    |                |
+----------+----------+------+-----+---------+----------------+
6 rows in set (0.004 sec)

透過 INSERT 新增加了五筆資料.

MariaDB [testdb]> INSERT INTO employee (Name , Dept , JobTitle , Salary , email) VALUES ('Ben' , 'Testing' , 'Engineer' , '45000' , 'ben@benjr.tw') , ('Afa' , 'Power' , 'Engineer' , '48000' , 'Afa@benjr.tw') , ('Boss' ,'Testing' , 'Manager' , '75000' , 'Boss@benjr.tw') , ('JoJo' , 'Testing' , 'Engineer' , '45000' , 'jojo@benjr.tw') ,  ('Ian' , 'PM' , 'Engineer' , '85000' , 'ian@benjr.tw');
Query OK, 5 rows affected (0.002 sec)
Records: 5  Duplicates: 0  Warnings: 0
 
MariaDB [testdb]> SELECT * FROM employee;
+----+------+---------+----------+--------+---------------+
| K1 | Name | Dept    | JobTitle | Salary | email         |
+----+------+---------+----------+--------+---------------+
|  1 | Ben  | Testing | Engineer |  45000 | ben@benjr.tw  |
|  2 | Afa  | Power   | Engineer |  48000 | Afa@benjr.tw  |
|  3 | Boss | Testing | Manager  |  75000 | Boss@benjr.tw |
|  4 | JoJo | Testing | Engineer |  45000 | jojo@benjr.tw |
|  5 | Ian  | PM      | Engineer |  85000 | ian@benjr.tw  |
+----+------+---------+----------+--------+---------------+
5 rows in set (0.001 sec)

• LAST_INSERT_ID
  當資料欄位為 AUTO_INCREMENT 時,新增資料後才會知道該數值,透過 LAST_INSERT_ID 函數,可以得知剛剛新增資料 AUTO_INCREMENT 的 ID 數值是多少 (當有多筆資料新增時,並不會影響彼此讀取自己新增資料的 ID).

  MariaDB [testdb]> INSERT INTO employee (Name , Dept , JobTitle , Salary , email) VALUES ('Mat' , 'Testing' , 'Engineer' , '39000' , 'mat@benjr.tw') ;
  Query OK, 1 row affected (0.002 sec)
  
  MariaDB [testdb]> SELECT LAST_INSERT_ID();
  +------------------+
  | LAST_INSERT_ID() |
  +------------------+
  |                6 |
  +------------------+
  1 row in set (0.001 sec)