INT(3) column not cliping the value to appropriate length and allowing the full value to be inserted - MySQL

问题

I have an INT(3) UNSIGNED column. If I insert a value with character length more that 3, it doesn't clip that value but inserts it.

Whats happening?

回答1:

FROM What does "size" in int(size) of MySQL mean?

Finally, let's come to the place of the manual where there is the biggest hint to what the number means:

Several of the data type descriptions use these conventions:

M indicates the maximum display width for integer types. For floating-point and fixed-point types, M is the total number of digits that can be stored. For string types, M is the maximum length. The maximum allowable value of M depends on the data type.

It's about the display width. The weird thing is, though2, that, for example, if you have a value of 5 digits in a field with a display width of 4 digits, the display width will not cut a digits off.

If the value has less digits than the display width, nothing happens either. So it seems like the display doesn't have any effect in real life.

Now2 ZEROFILL comes into play. It is a neat feature that pads values that are (here it comes) less than the specified display width with zeros, so that you will always receive a value of the specified length. This is for example useful for invoice ids.

So, concluding: The size is neither bits nor bytes. It's just the display width, that is used when the field has ZEROFILL specified.

mysql> create table a ( a tinyint );
Query OK, 0 rows affected (0.29 sec)
mysql> show columns from a;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| a | tinyint(4) | YES | | NULL | |
+-------+------------+------+-----+---------+-------+
1 row in set (0.26 sec)

mysql> alter table a change a a tinyint(1);
Query OK, 0 rows affected (0.09 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> insert into a values (100);
Query OK, 1 row affected (0.00 sec)

mysql> select * from a;
+-----+
| a |
+-----+
| 100 |
+-----+
1 row in set (0.00 sec)


2 Some code to better explain what I described so clumsily.
mysql> create table b ( b int (4));
Query OK, 0 rows affected (0.25 sec)

mysql> insert into b values (10000);
Query OK, 1 row affected (0.00 sec)

mysql> select * from b;
+-------+
| b |
+-------+
| 10000 |
+-------+
1 row in set (0.00 sec)

mysql> alter table b change b b int(11);
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from b;
+-------+
| b |
+-------+
| 10000 |
+-------+
1 row in set (0.00 sec)

mysql> alter table b change b b int(11) zerofill;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from b;
+-------------+
| b |
+-------------+
| 00000010000 |
+-------------+
1 row in set (0.00 sec)

mysql> alter table b change b b int(4) zerofill;
Query OK, 1 row affected (0.08 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from b;
+-------+
| b |
+-------+
| 10000 |
+-------+
1 row in set (0.00 sec)

mysql> alter table b change b b int(6) zerofill;
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from b;
+--------+
| b |
+--------+
| 010000 |
+--------+
1 row in set (0.00 sec)

回答2:

actually 3 there is a display width which works for ZEROFILL that pads zero on the right. It doesn't limit the capacity of the integer as it stores upto 4294967295 starting from zero.

example,

CREATE TABLE tableName
(
    x INT(3) ZEROFILL NOT NULL, 
    y INT NOT NULL
);

INSERT INTO tableName (x,y) VALUES
(1, 1),
(12, 12);

SELECT x, y FROM tableName;

Result:

  x          y
001          1
012         12

Using display width has no effect on how the data is stored. It affects only how it is displayed.

Integer Types (Exact Value)

来源：https://stackoverflow.com/questions/14664463/int3-column-not-cliping-the-value-to-appropriate-length-and-allowing-the-full

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mysql

int

unsigned