mysql字符集问题

########常用命令
mysql> show collation;
mysql> show character set;
mysql> show character set like '%utf8%';
mysql> show table status;

#########参数文件中定义
character_set_server=utf8mb4

默认

##########命令举例
mysql> use mysql
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> show character set like '%utf8%';
+---------+---------------+--------------------+--------+
| Charset | Description | Default collation | Maxlen |
+---------+---------------+--------------------+--------+
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |
+---------+---------------+--------------------+--------+
2 rows in set (0.00 sec)

mysql>

###行注释
Charset ： 字符集
Description 描述
Default collation ： 默认排序、插入检查规则 ci
Maxlen ： 最大长度

####################
●配置参数character_set_server
●CREATE DATABASE
●CREATE TABLE

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
[create_ specification] ...
create_ specification:
[DEFAULT] CHARACTER SET [=] charset_ name
CREATE TABLE t( a CHAR(10))CHARSET=utf8mb4;
| [DEFAULT] COLLATE [=] collation_ _name
CREATE TABLEt (
a VARCHAR(10) CHARSET gbk,
b VARCHAR (10) CHARSET latin1,
C VARCHAR (10) ) CHARSET=utf8mb4;

#########数据有效性约束：
ENUM & SET
●字符串类型--集合类型
●ENUM类型最多允许65536个值
●SET类型最多允许64个值
●通过sql_mode参数可以用于约束检查
mysql> CREATE TABLE t(
> user VARCHAR(30),
> sex ENUM('male',female')
->)ENGINE=InnoDB;
Query OK, 0 rows affected (0.01 sec)

mysql> SET sQL _MODE='strict _trans. _tables';
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO t SELECT "David",'male';
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> INSERT INTO t SELECT 'John','bimale';
ERROR 1265 (01000); Data truncated for column 'sex' at row 1

###############关于ENUM举例：#####################################

mysql> set sql_mode=''; #先不设置sql_mode
Query OK, 0 rows affected (0.00 sec)

mysql> create table a ( a enum ('m','f')); #创建一张表，字段类型为enum
Query OK, 0 rows affected (0.01 sec)

mysql> desc a; #查看这表
+-------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| a | enum('m','f') | YES | | NULL | |
+-------+---------------+------+-----+---------+-------+
1 row in set (0.00 sec)

mysql> insert into a select 'm'; #插入一个合法值
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from a; #查看
+------+
| a |
+------+
| m |
+------+
1 row in set (0.00 sec)

mysql> insert into a select 'y'; #插入一个非法值
Query OK, 1 row affected, 1 warning (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 1

mysql> select * from a; #查看，虽然没有报错，但是插入的是空值
+------+
| a |
+------+
| m |
| |
+------+
2 rows in set (0.00 sec)

mysql> set sql_mode='STRICT_TRANS_TABLES'; #修改sql_mode
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> insert into a select 'y'; #再插入一个非法值
ERROR 1265 (01000): Data truncated for column 'a' at row 1
mysql> select * from a; #查看，插入失败
+------+
| a |
+------+
| m |
| |
+------+
2 rows in set (0.00 sec)

mysql>

############时间#########################
占用字节 表示范围
DATETIME 8 1000-01-01 00:00:00 ~ 9999-12-31 23:59:59
DATE， 3 1000-01-01 ~ 9999-12-31
TIMESTAMP 4 1970-01-01 00:00:00 UTC ~2038-01-19 03:14:07 UTC
YEAR 1 YEAR(2): 1970 ~ 2070
YEAR(4): 1901 ~ 2155
TIME 3 -838:59:59 ~838:59:59

#TIMESTAMP有时区

####时区举例###################
mysql> drop table a;
Query OK, 0 rows affected (0.00 sec)

mysql> create table a (a TIMESTAMP,b datetime);
Query OK, 0 rows affected (0.00 sec)

mysql> desc a ;
+-------+-----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------+------+-----+---------+-------+
| a | timestamp | YES | | NULL | |
| b | datetime | YES | | NULL | |
+-------+-----------+------+-----+---------+-------+
2 rows in set (0.00 sec)

mysql> insert into a select now(),now();
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from a;
+---------------------+---------------------+
| a | b |
+---------------------+---------------------+
| 2020-04-20 12:46:44 | 2020-04-20 12:46:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)

mysql> select @@time_zone;
+-------------+
| @@time_zone |
+-------------+
| SYSTEM |
+-------------+
1 row in set (0.00 sec)

mysql> set time_zone='+00:00';
Query OK, 0 rows affected (0.00 sec)

mysql> select * from a;
+---------------------+---------------------+
| a | b |
+---------------------+---------------------+
| 2020-04-20 04:46:44 | 2020-04-20 12:46:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)