[mysql] MySql: Tinyint (2) vs tinyint(1) - what is the difference?

I knew boolean in mysql as tinyint (1).

Today I see a table with defined an integer like tinyint(2), and also others like int(4), int(6) ...

What does the size means in field of type integer and tinyint ?

About the INT, TINYINT... These are different data types, INT is 4-byte number, TINYINT is 1-byte number. More information here - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT.

The syntax of TINYINT data type is TINYINT(M), where M indicates the maximum display width (used only if your MySQL client supports it).

Numeric Type Attributes.

The (m) indicates the column display width; applications such as the MySQL client make use of this when showing the query results.

For example:

| v   | a   |  b  |   c |
+-----+-----+-----+-----+
| 1   | 1   |  1  |   1 |
| 10  | 10  | 10  |  10 |
| 100 | 100 | 100 | 100 |

Here a, b and c are using TINYINT(1), TINYINT(2) and TINYINT(3) respectively. As you can see, it pads the values on the left side using the display width.

It's important to note that it does not affect the accepted range of values for that particular type, i.e. TINYINT(1) still accepts [-128 .. 127].

mysql> CREATE TABLE tin3(id int PRIMARY KEY,val TINYINT(10) ZEROFILL);
Query OK, 0 rows affected (0.04 sec)

mysql> INSERT INTO tin3 VALUES(1,12),(2,7),(4,101);
Query OK, 3 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM tin3;
+----+------------+
| id | val        |
+----+------------+
|  1 | 0000000012 |
|  2 | 0000000007 |
|  4 | 0000000101 |
+----+------------+
3 rows in set (0.00 sec)

mysql>

mysql> SELECT LENGTH(val) FROM tin3 WHERE id=2;
+-------------+
| LENGTH(val) |
+-------------+
|          10 |
+-------------+
1 row in set (0.01 sec)


mysql> SELECT val+1 FROM tin3 WHERE id=2;
+-------+
| val+1 |
+-------+
|     8 |
+-------+
1 row in set (0.00 sec)