MySQL 数据类型之日期时间类型

• 日期时间类型包括date,time,datetime,timestamp和year，用来指定不同范围的日期或时间值
• Date类型用来表示仅日期，MySQL默认的日期格式为yyyy-mm-dd，取值范围为1000-01-01到9999-12-31
• Datetime类型用来表示日期和时间，MySQL默认的格式为yyyy-mm-dd hh:mi:ss，取值范围为1000-01-01 00:00:00到9999-12-31 23:59:59
• Timestamp类型也用来表示日期和时间，其取值范围为1970-01-01 00:00:01到2038-01-19 03:14:07
• Datetime和timestamp两个类型都可以保存到微妙级别，即6位毫秒微妙精度，即1000-01-01 00:00:00.000000到9999-12-31 23:59:59.999999和1970-01-01 00:00:01.000000到2038-01-19 03:14:07.999999
• 非法的date,datetime,timestamp值将被转换成0值，0000-00-00或者0000-00-00 00:00:00

mysql> select current_date();
+----------------+
| current_date() |
+----------------+
| 2020-04-21     |
+----------------+
1 row in set (0.00 sec)

mysql> select current_datetime();
ERROR 1305 (42000): FUNCTION course.current_datetime does not exist
mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2020-04-21 21:40:48 |
+---------------------+
1 row in set (0.00 sec)

mysql> create table temp5(tstamp datetime,tstamp2 timestamp);
Query OK, 0 rows affected (0.17 sec)

mysql> insert into temp5 values(now(),now());
Query OK, 1 row affected (0.04 sec)

mysql> select * from temp5;
+---------------------+---------------------+
| tstamp              | tstamp2             |
+---------------------+---------------------+
| 2020-04-21 21:42:31 | 2020-04-21 21:42:31 |
+---------------------+---------------------+
1 row in set (0.00 sec)

mysql> insert into temp5 values('2020-04-22 21:45:10.321123',now());
Query OK, 1 row affected (0.01 sec)

mysql> select * from temp5;
+---------------------+---------------------+
| tstamp              | tstamp2             |
+---------------------+---------------------+
| 2020-04-21 21:42:31 | 2020-04-21 21:42:31 |
| 2020-04-22 21:45:10 | 2020-04-21 21:45:13 |
+---------------------+---------------------+
2 rows in set (0.00 sec)

mysql> drop table temp5;
Query OK, 0 rows affected (0.08 sec)

mysql> create table temp5(tstamp datetime(6),tstamp2 timestamp(3));
Query OK, 0 rows affected (0.11 sec)

mysql> insert into temp5 values('2020-04-22 21:45:10.321123','2020-04-22 21:45:10.321123'); 
Query OK, 1 row affected (0.09 sec)

mysql> select * from temp5;
+----------------------------+-------------------------+
| tstamp                     | tstamp2                 |
+----------------------------+-------------------------+
| 2020-04-22 21:45:10.321123 | 2020-04-22 21:45:10.321 |
+----------------------------+-------------------------+
1 row in set (0.00 sec)

• Time类型用来仅表示时间，MySQL默认格式为HH:MM:SS，其取值范围为-838:59:59到838:59:59，小时字段可以超过24是因为time类型不光代表小时，也可以代表持续时长中的小时
• Time类型也可以包含6位的毫秒微秒精度，其取值范围为-838:59:59.000000到838:59:59.000000
• Year类型用来仅表示年份，MySQL默认格式为YYYY，其取值范围为1901到2155，和0000
• 针对非法的year数据，则直接转化为0000

mysql> select date_add(now(),interval 50 hour);
+----------------------------------+
| date_add(now(),interval 50 hour) |
+----------------------------------+
| 2020-04-23 23:52:01              |
+----------------------------------+
1 row in set (0.00 sec)

mysql> select now(),date_add(now(),interval 50 hour);
+---------------------+----------------------------------+
| now()               | date_add(now(),interval 50 hour) |
+---------------------+----------------------------------+
| 2020-04-21 21:52:14 | 2020-04-23 23:52:14              |
+---------------------+----------------------------------+
1 row in set (0.00 sec)

• Timestamp和datetime日期时间类型可以被自动初始化和更新为当前的日期时间数据，当你默认指定current timestamp为默认值，或者指定此数据列为自动更新时
　　• 指定默认值是指当插入新的数据而该列没有显视指定数值时，则插入当前日期时间值
　　• 指定自动更新是指当行中的其他列被更新时，则此列被自动更新为当前日期时间值

mysql> drop table temp5;
Query OK, 0 rows affected (0.10 sec)

mysql> create table temp5(id int,tstamp datetime default current_timestamp on update current_timestamp,tstamp2 timestamp default current_timestamp on update current_timestamp);
Query OK, 0 rows affected (0.07 sec)

mysql> alter table temp5 add name varchar(64);
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc temp5;
+---------+-------------+------+-----+-------------------+-----------------------------------------------+
| Field   | Type        | Null | Key | Default           | Extra                                         |
+---------+-------------+------+-----+-------------------+-----------------------------------------------+
| id      | int(11)     | YES  |     | NULL              |                                               |
| tstamp  | datetime    | YES  |     | CURRENT_TIMESTAMP | DEFAULT_GENERATED on update CURRENT_TIMESTAMP |
| tstamp2 | timestamp   | YES  |     | CURRENT_TIMESTAMP | DEFAULT_GENERATED on update CURRENT_TIMESTAMP |
| name    | varchar(64) | YES  |     | NULL              |                                               |
+---------+-------------+------+-----+-------------------+-----------------------------------------------+
4 rows in set (0.01 sec)

mysql> select current_timestamp;
+---------------------+
| current_timestamp   |
+---------------------+
| 2020-04-21 22:03:29 |
+---------------------+
1 row in set (0.01 sec)

mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2020-04-21 22:03:35 |
+---------------------+
1 row in set (0.00 sec)

mysql> select * from temp5;
Empty set (0.00 sec)

mysql> insert into temp5(id,name) values(1,'a');
Query OK, 1 row affected (0.04 sec)

mysql> select * from temp5;
+------+---------------------+---------------------+------+
| id   | tstamp              | tstamp2             | name |
+------+---------------------+---------------------+------+
|    1 | 2020-04-21 22:05:11 | 2020-04-21 22:05:11 | a    |
+------+---------------------+---------------------+------+
1 row in set (0.00 sec)

mysql> insert into temp5(id,name) values(2,'b');
Query OK, 1 row affected (0.05 sec)

mysql> select * from temp5;
+------+---------------------+---------------------+------+
| id   | tstamp              | tstamp2             | name |
+------+---------------------+---------------------+------+
|    1 | 2020-04-21 22:05:11 | 2020-04-21 22:05:11 | a    |
|    2 | 2020-04-21 22:05:43 | 2020-04-21 22:05:43 | b    |
+------+---------------------+---------------------+------+
2 rows in set (0.00 sec)

mysql> update temp5 set name='abc';
Query OK, 2 rows affected (0.07 sec)
Rows matched: 2  Changed: 2  Warnings: 0

mysql> select * from temp5;
+------+---------------------+---------------------+------+
| id   | tstamp              | tstamp2             | name |
+------+---------------------+---------------------+------+
|    1 | 2020-04-21 22:06:05 | 2020-04-21 22:06:05 | abc  |
|    2 | 2020-04-21 22:06:05 | 2020-04-21 22:06:05 | abc  |
+------+---------------------+---------------------+------+
2 rows in set (0.00 sec)

mysql> drop table temp5;
Query OK, 0 rows affected (0.14 sec)

mysql> create table temp5(id int,tstamp datetime default now());
Query OK, 0 rows affected (0.09 sec)

mysql> desc temp5;
+--------+----------+------+-----+-------------------+-------------------+
| Field  | Type     | Null | Key | Default           | Extra             |
+--------+----------+------+-----+-------------------+-------------------+
| id     | int(11)  | YES  |     | NULL              |                   |
| tstamp | datetime | YES  |     | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
+--------+----------+------+-----+-------------------+-------------------+
2 rows in set (0.00 sec)

mysql> drop table temp5;
Query OK, 0 rows affected (0.13 sec)

mysql> create table temp5(id int,tstamp datetime default date_add(now(),interval 1 day));    # 5.7版本及以前
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'date_add(now(),interval 1 day))' at line 1
mysql> select date_add(now(),interval 1 day);
+--------------------------------+
| date_add(now(),interval 1 day) |
+--------------------------------+
| 2020-04-22 22:11:52            |
+--------------------------------+
1 row in set (0.00 sec)

mysql> create table temp5(id int,tstamp datetime default (date_add(now(),interval 1 day)));  # 8.0版本
Query OK, 0 rows affected (0.16 sec)

mysql> desc temp5;
+--------+----------+------+-----+--------------------------+-------------------+
| Field  | Type     | Null | Key | Default                  | Extra             |
+--------+----------+------+-----+--------------------------+-------------------+
| id     | int(11)  | YES  |     | NULL                     |                   |
| tstamp | datetime | YES  |     | (now() + interval 1 day) | DEFAULT_GENERATED |
+--------+----------+------+-----+--------------------------+-------------------+
2 rows in set (0.00 sec)

mysql> insert into temp5(id) values(1);
Query OK, 1 row affected (0.06 sec)

mysql> select * from temp5;
+------+---------------------+
| id   | tstamp              |
+------+---------------------+
|    1 | 2020-04-22 22:13:27 |
+------+---------------------+
1 row in set (0.00 sec)

mysql> drop table temp;
Query OK, 0 rows affected (0.04 sec)

mysql> create table temp(id int,id2 int default (1+1));
Query OK, 0 rows affected (0.13 sec)

mysql> desc temp;
+-------+---------+------+-----+---------+-------------------+
| Field | Type    | Null | Key | Default | Extra             |
+-------+---------+------+-----+---------+-------------------+
| id    | int(11) | YES  |     | NULL    |                   |
| id2   | int(11) | YES  |     | (1 + 1) | DEFAULT_GENERATED |
+-------+---------+------+-----+---------+-------------------+
2 rows in set (0.01 sec)

mysql> insert into temp(id) values(10);
Query OK, 1 row affected (0.08 sec)

mysql> select * from temp;
+------+------+
| id   | id2  |
+------+------+
|   10 |    2 |
+------+------+
1 row in set (0.00 sec)