之前我们介绍了:MySQL数据库TIMESTAMP设置默认值的灵活运用,本次我们接着上次的内容介绍几个MySQL数据库TIMESTAMP设置默认值的几个应用实例,希望能够对您有所帮助。
#1查看表定义,可以看到b列有个属性ON UPDATE CURRENT_TIMESTAMP,导致更新数据时,即便未涉及到该列,该列数据也被自动更新。另一方面,c列默认值是'0000-00-00 00:00:00',实际插入已经被自动赋值为current_timestamp。
root@localhost:test >show create table dj1\G
*************************** 1. row ***************************
Table: dj1
Create Table: CREATE TABLE `dj1` (
`a` char(1) COLLATE utf8_bin DEFAULT NULL,
`b` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`c` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
UNIQUE KEY `dj1_idx_u1` (`b`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin
1 row in set (0.00 sec)
#2创建表dj2,列b不带自动更新属性。
root@localhost:test >CREATE TABLE `dj2` (
-> `a` char(1) COLLATE utf8_bin DEFAULT NULL,
-> `b` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ,
-> `c` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
-> UNIQUE KEY `dj1_idx_u1` (`b`)
-> ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
Query OK, 0 rows affected (0.01 sec)
#3插入dj2测试数据
root@localhost:test >insert into dj2 values (1,null,null);
Query OK, 1 row affected (0.00 sec)
root@localhost:test >insert into dj2 values (2,null,null);
Query OK, 1 row affected (0.00 sec)
#4查看dj2数据
root@localhost:test >select * from dj2;
+------+---------------------+---------------------+
| a | b | c |
+------+---------------------+---------------------+
| 1 | 2009-09-09 14:02:55 | 2009-09-09 14:02:55 |
| 2 | 2009-09-09 14:03:00 | 2009-09-09 14:03:00 |
+------+---------------------+---------------------+
2 rows in set (0.00 sec)
#5dj2上创建唯一索引
root@localhost:test >create unique index dj2_idx_u1 on dj2(b);
Query OK, 2 rows affected (0.02 sec)
Records: 2 Duplicates: 0 Warnings: 0
#更新数据成功
root@localhost:test >update dj2 set a=9;
Query OK, 2 rows affected (0.00 sec)
Rows matched: 2 Changed: 2 Warnings: 0
root@localhost:test >select * from dj2;
+------+---------------------+---------------------+
| a | b | c |
+------+---------------------+---------------------+
| 9 | 2009-09-09 14:02:55 | 2009-09-09 14:02:55 |
| 9 | 2009-09-09 14:03:00 | 2009-09-09 14:03:00 |
+------+---------------------+---------------------+
2 rows in set (0.00 sec)
#6创建表dj3,b列默认值为CURRENT_TIMESTAMP,c列默认值为CURRENT_TIMESTAMP带自动更新属性,报错,不允许行为。
root@localhost:test >CREATE TABLE `dj3` (
-> `a` char(1) COLLATE utf8_bin DEFAULT NULL,
-> `b` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ,
-> `c` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
-> UNIQUE KEY `dj1_idx_u1` (`b`)
-> ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
ERROR 1293 (HY000): Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT or ON UPDATE clause
#7创建表dj4,b列默认值为CURRENT_TIMESTAMP,c列默认值为'0000-00-00 00:00:00'带自动更新属性,报错,不允许行为。
root@localhost:test >CREATE TABLE `dj4` (
-> `a` char(1) COLLATE utf8_bin DEFAULT NULL,
-> `b` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ,
-> `c` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP,
-> UNIQUE KEY `dj1_idx_u1` (`b`)
-> ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
ERROR 1293 (HY000): Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT or ON UPDATE clause
#8创建表dj5,b列默认值为CURRENT_TIMESTAMP带自动更新属性,c列默认值为CURRENT_TIMESTAMP,报错源码天空,不允许行为。
root@localhost:test >CREATE TABLE `dj5` (
-> `a` char(1) COLLATE utf8_bin DEFAULT NULL,
-> `b` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
-> `c` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ,
-> UNIQUE KEY `dj1_idx_u1` (`b`)
-> ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
ERROR 1293 (HY000): Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT or ON UPDATE clause
以上就是MySQL数据库TIMESTAMP设置默认值的几个应用实例,本文就介绍到这里,希望本次的介绍能够对您有所收获!