mysql 5.5与5.6 timestamp 字段 DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP的区别

作者：袖梨 2022-11-14

mysql5.6数据库:

代码如下 复制代码
[BIGHD]([email protected]) [cm]> SELECT version();
+------------+
| version() |
+------------+
| 5.6.13-log |
+------------+
1 ROW IN SET (0.02 sec)

[BIGHD]([email protected]) [cm]> ALTER TABLE s__uk ADD `last_op_time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP;
Query OK, 0 ROWS affected (0.99 sec)
Records: 0 Duplicates: 0 Warnings: 0

[BIGHD]([email protected]) [cm]> SELECT id, last_op_time FROM s__uk LIMIT 1;
+----+---------------------+
| id | last_op_time |
+----+---------------------+
| 1 | 2013-10-10 10:17:57 |
+----+---------------------+
1 ROW IN SET (0.00 sec)




mysql5.5数据库:

代码如下 复制代码

(root@localhost) [cm]> SELECT version();
+------------+
| version() |
+------------+
| 5.5.15-log |
+------------+
1 ROW IN SET (0.00 sec)

(root@localhost) [cm]> ALTER TABLE s__uk ADD `last_op_time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP;
Query OK, 2523 ROWS affected (0.99 sec)
Records: 2523 Duplicates: 0 Warnings: 0

(root@localhost) [cm]> SELECT last_op_time FROM s__uk LIMIT 1;
+---------------------+
| last_op_time |
+---------------------+
| 0000-00-00 00:00:00 |
+---------------------+
1 ROW IN SET (0.00 sec)

另外，有没有考虑过如果只更新这个字段会怎样？会是指定的时间，还是自动生成的时间？

代码如下 复制代码
(root@localhost) [cm]> UPDATE s__uk SET last_op_time='2012-12-12 00:00:00' WHERE id=1;
Query OK, 1 ROW affected (0.07 sec)
ROWS matched: 1 Changed: 1 Warnings: 0

(root@localhost) [cm]> SELECT id, last_op_time FROM s__uk LIMIT 1;
+----+---------------------+
| id | last_op_time |
+----+---------------------+
| 1 | 2012-12-12 00:00:00 |
+----+---------------------+
1 ROW IN SET (0.01 sec)

猜对了木有？

PS:
如何判断字段中是否有多字节字符（比如中文）?

CHARACTER_LENGTH(value) = length(value) 则不包含多字节字符。

length为字节Bytes长度， CHARACTER_LENGTH为字符characters长度。

PS2:
mongodb find()

之后美化/格式化输出的函数是：
db.tbl.find().pretty()

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