The display width does not constrain the range of values that can be stored in the column, nor the number of digits that are displayed for values having a width exceeding that specified for the column. For example, a column specified as SMALLINT(3) has the usual SMALLINT range of -32768 to 32767, and values outside the range allowed by three characters are displayed using more than three characters.
So, if display width doesn’t constrain the range of values our numeric type can hold, why to use it at all? On MySQL forum, there was a post suggesting that by using the display width, we set mental reminder to ourselves on how big the field should be. Me personally, find this quite logical, this is some kind of mental tooltip which pops up when you review your schema.
Source from: PHP Magazine
| Type | Bytes | Minimum Value | Maximum Value |
| (Signed/Unsigned) | (Signed/Unsigned) | ||
TINYINT | 1 | -128 | 127 |
0 | 255 | ||
SMALLINT | 2 | -32768 | 32767 |
0 | 65535 | ||
MEDIUMINT | 3 | -8388608 | 8388607 |
0 | 16777215 | ||
INT | 4 | -2147483648 | 2147483647 |
0 | 4294967295 | ||
BIGINT | 8 | -9223372036854775808 | 9223372036854775807 |
0 | 18446744073709551615 |
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