软件测试修炼之路 A Tester

MySQL-数据类型和操作数据库表

2016-07-19
Dex

数据类型

数据类型是指列、存储过程参数、表达式和局部变量的数据特征,它决定了数据的存储格式,代表了不同的信息类型。

数据类型之整型

整型

数据类型之浮点型

float和double对比

数据类型之日期时间型

date型

数据类型之字符型

字符型

创建数据表

数据表(或称表)是数据库最重要的组成成分之一,是其他对象的基础。

打开数据库命令:USE 数据库名称;

mysql> USE test;
Database changed

查看当前使用的是哪一个数据库,命令:

mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| test       |
+------------+
1 row in set (0.00 sec)

创建数据表语法:

CREATE TABLE [IF NOT EXISTS] table_name (
	column_name data_type,
	...
)

创建tb1表:

mysql> CREATE TABLE tb1(
    -> username VARCHAR(20),
    -> age TINYINT UNSIGNED,
    -> salary FLOAT(8,2) UNSIGNED
    -> );
Query OK, 0 rows affected (0.91 sec)

查看数据表

查看数据表列表语法:

SHOW TABLES [FROM db_name] [LIKE 'pattern' | WHERE expr]

在当前库下,执行命令:

mysql> SHOW TABLES;
+----------------+
| Tables_in_test |
+----------------+
| tb1            |
+----------------+
1 row in set (0.01 sec)

查看其他数据库下的数据表:

mysql> SHOW TABLES FROM t2;
Empty set (0.00 sec)

查看其他数据库下的表,并不会改变当前应用的库:

mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| test       |
+------------+
1 row in set (0.00 sec)

mysql> SHOW TABLES;
+----------------+
| Tables_in_test |
+----------------+
| tb1            |
+----------------+
1 row in set (0.00 sec)

查看数据表结构

查看数据表结构语法:

SHOW COLUMNS FROM tbl_name;

执行命令:

mysql> SHOW COLUMNS FROM tb1;
+----------+---------------------+------+-----+---------+-------+
| Field    | Type                | Null | Key | Default | Extra |
+----------+---------------------+------+-----+---------+-------+
| username | varchar(20)         | YES  |     | NULL    |       |
| age      | tinyint(3) unsigned | YES  |     | NULL    |       |
| salary   | float(8,2) unsigned | YES  |     | NULL    |       |
+----------+---------------------+------+-----+---------+-------+
3 rows in set (0.25 sec)

记录的插入与查找

INSERT

插入记录语法:

INSERT [INTO] tbl_name [(col_name,...)] VALUES(val,...)

执行命令:

mysql> INSERT tb1 VALUES('Tom',25,7863.25);
Query OK, 1 row affected (0.16 sec)

VALUES值少一个后,执行:

mysql> INSERT tb1 VALUES('Tom',25);
ERROR 1136 (21S01): Column count doesn't match value count at row 1

省略列名的情况下,必须输入所有的VALUES值。

只插入一个字段:

mysql> INSERT tb1(username,salary) VALUES('John',4500.69);
Query OK, 1 row affected (0.06 sec)

SELECT

记录查找语法:

SELECT expr,... FROM tbl_name;

执行命令:

mysql> SELECT * FROM tb1;
+----------+------+---------+
| username | age  | salary  |
+----------+------+---------+
| Tom      |   25 | 7863.25 |
| John     | NULL | 4500.69 |
+----------+------+---------+
2 rows in set (0.01 sec)

空值与非空

  • NULL, 字段值可以为空;
  • NOT NULL, 字段值禁止为空;

执行命令:

mysql> CREATE TABLE tb2(
    -> username VARCHAR(20) NOT NULL,
    -> age TINYINT UNSIGNED NULL
    -> );
Query OK, 0 rows affected (0.11 sec)

mysql> SHOW COLUMNS FROM tb2;
+----------+---------------------+------+-----+---------+-------+
| Field    | Type                | Null | Key | Default | Extra |
+----------+---------------------+------+-----+---------+-------+
| username | varchar(20)         | NO   |     | NULL    |       |
| age      | tinyint(3) unsigned | YES  |     | NULL    |       |
+----------+---------------------+------+-----+---------+-------+
2 rows in set (0.01 sec)

mysql> INSERT tb2 VALUES('TOM',NULL);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM tb2;
+----------+------+
| username | age  |
+----------+------+
| TOM      | NULL |
+----------+------+
1 row in set (0.00 sec)

如果非空项输入NULL,会报错:

mysql> INSERT tb2 VALUES(NULL,22);
ERROR 1048 (23000): Column 'username' cannot be null

自动编号

AUTO_INCREMENT

  • 自动编号,且必须与主键组合使用
  • 默认情况下,起始值为1,每次的增量为1

      mysql> CREATE TABLE tb3(
          -> id SMALLINT UNSIGNED AUTO_INCREMENT,
          -> username VARCHAR(30) NOT NULL
          -> );
      ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
    

提示必须定义一个主键。

初涉主键约束

PRIMARY KEY

  • 主键约束
  • 每张数据表只能存在一个主键
  • 主键保证记录的唯一性
  • 主键自动为NOT NULL

      mysql> CREATE TABLE tb3(
          -> id SMALLINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
          -> username VARCHAR(30) NOT NULL
          -> );
      Query OK, 0 rows affected (0.04 sec)
    
      mysql> SHOW COLUMNS FROM tb3;
      +----------+----------------------+------+-----+---------+----------------+
      | Field    | Type                 | Null | Key | Default | Extra          |
      +----------+----------------------+------+-----+---------+----------------+
      | id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
      | username | varchar(30)          | NO   |     | NULL    |                |
      +----------+----------------------+------+-----+---------+----------------+
      2 rows in set (0.00 sec)
    

依次插入一条条数据:

mysql> INSERT tb3(username) VALUES('Tom');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT tb3(username) VALUES('John');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT tb3(username) VALUES('Rose');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT tb3(username) VALUES('Dimitar');
Query OK, 1 row affected (0.00 sec)

查看自增的id字段:

mysql> SELECT * FROM tb3;
+----+----------+
| id | username |
+----+----------+
|  1 | Tom      |
|  2 | John     |
|  3 | Rose     |
|  4 | Dimitar  |
+----+----------+
4 rows in set (0.00 sec)

主键的唯一性:

mysql> CREATE TABLE tb4(
    -> id SMALLINT UNSIGNED PRIMARY KEY,
    -> username VARCHAR(30) NOT NULL
    -> );
Query OK, 0 rows affected (0.05 sec)

mysql> SHOW COLUMNS FROM tb4;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    |       |
| username | varchar(30)          | NO   |     | NULL    |       |
+----------+----------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

mysql> INSERT tb4 VALUES(22,'Tom');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT tb4 VALUES(4,'John');
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM tb4;
+----+----------+
| id | username |
+----+----------+
|  4 | John     |
| 22 | Tom      |
+----+----------+
2 rows in set (0.00 sec)

mysql> INSERT tb4 VALUES(22,'Rose');
ERROR 1062 (23000): Duplicate entry '22' for key 'PRIMARY'

初涉唯一约束

UNIQUE KEY

  • 唯一约束
  • 唯一约束可以保证记录的唯一性
  • 唯一约束的字段可以为空值(NULL)
  • 每张数据表可以存在多个唯一约束

      mysql> CREATE TABLE tb5
          -> (
          -> id SMALLINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
          -> username VARCHAR(30) NOT NULL UNIQUE KEY,
          -> age TINYINT UNSIGNED
          -> );
      Query OK, 0 rows affected (0.05 sec)
    
      mysql> SHOW COLUMNS FROM tb5;
      +----------+----------------------+------+-----+---------+----------------+
      | Field    | Type                 | Null | Key | Default | Extra          |
      +----------+----------------------+------+-----+---------+----------------+
      | id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
      | username | varchar(30)          | NO   | UNI | NULL    |                |
      | age      | tinyint(3) unsigned  | YES  |     | NULL    |                |
      +----------+----------------------+------+-----+---------+----------------+
      3 rows in set (0.01 sec)
    

插入同样的数据会报错:

mysql> INSERT tb5(username,age) VALUES('Tom',22);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT tb5(username,age) VALUES('Tom',22);
ERROR 1062 (23000): Duplicate entry 'Tom' for key 'username'

初涉默认约束

DEFAULT

  • 默认值
  • 当插入记录时,如果没有明确为字段赋值,则自动赋予默认值。

      mysql> CREATE TABLE tb6(
          -> id SMALLINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
          -> username VARCHAR(20) NOT NULL UNIQUE KEY,
          -> sex ENUM('1','2','3') DEFAULT '3'
          -> );
      Query OK, 0 rows affected (0.12 sec)
    
      mysql> SHOW COLUMNS FROM tb6;
      +----------+----------------------+------+-----+---------+----------------+
      | Field    | Type                 | Null | Key | Default | Extra          |
      +----------+----------------------+------+-----+---------+----------------+
      | id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
      | username | varchar(20)          | NO   | UNI | NULL    |                |
      | sex      | enum('1','2','3')    | YES  |     | 3       |                |
      +----------+----------------------+------+-----+---------+----------------+
      3 rows in set (0.00 sec)
    

只插入username,表中的sex字段默认为3

mysql> INSERT tb6(username) VALUES('Tom');
Query OK, 1 row affected (0.04 sec)

mysql> SELECT * FROM tb6;
+----+----------+------+
| id | username | sex  |
+----+----------+------+
|  1 | Tom      | 3    |
+----+----------+------+
1 row in set (0.00 sec)

总结

  • 数据类型
    • 字符型
    • 整型
    • 浮点型
    • 日期时间型
  • 数据表操作
    • 插入记录
    • 查找记录
  • 记录操作
    • 创建数据表
    • 约束的使用

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