MySQL 数据类型-2

数据类型

数值类型

整型
-TINYINT -SMALLINT -MEDIUMINT -INT -BIGINT

关键词：ZEROFILL（零填充） 、 UNSIGNED（无符号） 、 AUTO_INCREMENT（自动递增） 、 NOT NULL（非空） 、 PRIMARY KEY（主键） 、 UNIQUE（外键）

1）定义了ZEAROFILL的都自动添加unsigned 属性。
2）任何想要使用auto_increment的列，应定义NOT NULL ,并定义为 primary key或者是unique。

mysql> CREATE TABLE t1(
    -> id1 INT,
    -> id2 INT(5));

数值类型.png

浮点数

浮点数和定点数
单精度：FLOAT(X,Y) 双精度：DOUBLE(X,Y) 定点：DECIMAL(X,Y)

浮点数如果不写精度，就按照输入的精度显示，定点数如果不写精度，就按照DECIMAL(10，0)

浮点数和定点数.png

日期和时间类型

-DATE
-DATETIME
-TIMESTAMP
-TIME
-YEAR

日期和时间类型.png

日期和时间类型.png

DATETIME是DATE和TIME的组合

mysql> DROP TABLE t1;
mysql> CREATE TABLE t (
    -> d date,
    -> t time,
    -> dt datetime);
mysql> DESC t;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| d     | date     | YES  |     | NULL    |       |
| t     | time     | YES  |     | NULL    |       |
| dt    | datetime | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
mysql> INSERT INTO t(d,t,dt) VALUES(NOW(),NOW(),NOW());
mysql> SELECT * FROM t;
+------------+----------+---------------------+
| d          | t        | dt                  |
+------------+----------+---------------------+
| 2017-08-22 | 07:29:58 | 2017-08-22 07:29:58 |
+------------+----------+---------------------+

TIMESTAMP 时间戳

MySQL中只能有一列默认为CURRENT_TIMESTAMP；另外TIMESTAMP与时区有关，当插入时间时会先转换为本地时间存储，所以同一个时间在不同地区看到的时间可能不是一样的。

mysql> ALTER TABLE t ADD id1 TIMESTAMP;
mysql> SELECT * FROM t;

+------------+----------+---------------------+---------------------+
| d          | t        | dt                  | id1                 |
+------------+----------+---------------------+---------------------+
| 2017-08-22 | 07:29:58 | 2017-08-22 07:29:58 | 2017-08-22 07:38:20 |
+------------+----------+---------------------+---------------------+
mysql> ALTER TABLE t ADD id2 TIMESTAMP;
mysql> SELECT * FROM t;
+------------+----------+---------------------+---------------------+---------------------+
| d          | t        | dt                  | id1                 | id2                 |
+------------+----------+---------------------+---------------------+---------------------+
| 2017-08-22 | 07:29:58 | 2017-08-22 07:29:58 | 2017-08-22 07:38:20 | 0000-00-00 00:00:00 |
+------------+----------+---------------------+---------------------+---------------------+

时区相关

创建表
mysql> CREATE TABLE t8(
    -> id1 TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    -> id2 DATETIME DEFAULT NULL);
**查看当前时区**
mysql> SHOW VARIABLES LIKE "TIME_ZONE";
+---------------+--------+
| Variable_name | Value  |
+---------------+--------+
| time_zone     | SYSTEM |
+---------------+--------+

mysql> INSERT INTO t8 VALUES(NOW(),NOW());
mysql> SELECT * FROM t8;
+---------------------+---------------------+
| id1                 | id2                 |
+---------------------+---------------------+
| 2017-08-22 07:55:17 | 2017-08-22 07:55:17 |
+---------------------+---------------------+

**修改为东九区**
mysql> SET TIME_ZONE='+9:00';
mysql> SELECT * FROM t8;
+---------------------+---------------------+
| id1                 | id2                 |
+---------------------+---------------------+
| 2017-08-22 08:55:17 | 2017-08-22 07:55:17 |
+---------------------+---------------------+

时间戳说明

字符串类型###

-CHAR
-VARCHAR
-BINARY
-VARBINARY
-BLOB
-TEXT
-ENUM
-SET

字符类型

CHAR VARCHAR类型
NULL
BINARY VARBINARY类型
NULL
ENUM类型（枚举类型）

枚举类型

mysql> CREATE TABLE t(
    -> id INT(10) AUTO_INCREMENT PRIMARY KEY,
    -> sex ENUM("male","female")
    -> );

mysql> DESC t;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type                  | Null | Key | Default | Extra          |
+-------+-----------------------+------+-----+---------+----------------+
| id    | int(10)               | NO   | PRI | NULL    | auto_increment |
| sex   | enum('male','female') | YES  |     | NULL    |                |
+-------+-----------------------+------+-----+---------+----------------+

只允许从值的集合中选取值，而且不能一次取多个值

mysql> INSERT INTO t(sex) VALUES(NULL),("male"),("female"),("A");
ERROR 1265 (01000): Data truncated for column 'sex' at row 4

mysql> INSERT INTO t(sex) VALUES(NULL),("male"),("female");
mysql> SELECT * FROM t;
+----+--------+
| id | sex    |
+----+--------+
|  1 | NULL   |
|  2 | male   |
|  3 | female |
+----+--------+

SET类型

set类型

   为表t增加字段love
mysql> ALTER TABLE t ADD love SET("A","B","C");
mysql> UPDATE t SET love="a" WHERE id = 1;
mysql> SELECT * FROM t;
+----+--------+------+
| id | sex    | love |
+----+--------+------+
|  1 | NULL   | NULL |
|  2 | male   | NULL |
|  3 | female | NULL |
+----+--------+------+
   修改id=1的love的值
mysql> UPDATE t SET love="a" WHERE id = 1;
mysql> SELECT * FROM t;
+----+--------+------+
| id | sex    | love |
+----+--------+------+
|  1 | NULL   | A    |
|  2 | male   | NULL |
|  3 | female | NULL |
+----+--------+------+

   love=2 的时候一样可以修改记录
mysql> UPDATE t SET love=2 WHERE id = 1;
mysql> SELECT * FROM t;
+----+--------+------+
| id | sex    | love |
+----+--------+------+
|  1 | NULL   | B    |
|  2 | male   | NULL |
|  3 | female | NULL |
+----+--------+------+