What is the difference between int (1) and int (10)? Senior developers can't tell!

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confused

I have a problem recently , If you have a watch, you need to add user_id Field ,user_id Fields can be very large , So I mentioned mysql The repair order alter table xxx ADD user_id int(1). The leader saw my sql The repair order , So he said ： this int(1) I'm afraid it's not enough , Next is an explanation .

In fact, this is not the first time I have encountered such a problem , Many of them have jobs 5 An old driver of more than years . Including I often see that my colleagues have been using int(10), It feels like it's working int(1), The upper limit of the field is limited , This is certainly not the case .

Data speak

We know that mysql in int Occupy 4 Bytes , So for unsigned int, The maximum is 2^32-1 = 4294967295, nearly 40 Billion , Did you use it int(1), Can't you reach this maximum ？

CREATE TABLE `user` (
  `id` int(1) unsigned NOT NULL AUTO_INCREMENT,
   PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4;

id The field is unsigned int(1), Let me insert a maximum to see .

mysql> INSERT INTO `user` (`id`) VALUES (4294967295);
Query OK, 1 row affected (0.00 sec)

You can see the success , explain int Back number , No effect int Size supported by itself ,int(1)、int(2)...int(10) No difference .

Zero fill

commonly int Back number , coordination zerofill It works when used together . Let's take an example ：

CREATE TABLE `user` (
  `id` int(4) unsigned zerofill NOT NULL AUTO_INCREMENT,
   PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4;

Be careful int(4) There's a... In the back zerofill, Let's insert 4 Data .

mysql> INSERT INTO `user` (`id`) VALUES (1),(10),(100),(1000);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

Insert separately 1、10、100、1000 4 Data , Then let's check ：

mysql> select * from user;
+------+
| id   |
+------+
| 0001 |
| 0010 |
| 0100 |
| 1000 |
+------+
4 rows in set (0.00 sec)

Through the data, we can find int(4) + zerofill Realized the deficiency 4 Place complement 0 The phenomenon of , only int(4) It's no use .

And for 0001 such , The underlying storage is still 1, Just in the show will make up 0.

summary

int The following number cannot represent the length of the field ,int(num) General plus zerofill, It works .zerofill The function of can generally be used in some numbers related to numbers , For example, the student's number 001 002 ... 999 such , If mysql There is no function of zero padding , But when you have to format and output numbers of equal length , Then you have to deal with it yourself .

source ：juejin.cn/post/6992574502282477605

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