（My）SQL：声明的SMALLINT（4）和INT（4）之间的负载差异是实数吗？

Question

According to this (Dutch) webpage , one should use SMALLINT if the expected number will not exceed 9999 (4 digits), because INT would reserve too much system resources (free interpretation). But does that still count if the digits are limited, as in SMALLINT(4) and INT(4) ?

Answer 1

Firstly, the upper limit of a SMALLINT is not 9999 but 32767 - numbers are not stored in decimal, so the number of digits in the decimal representation of a number is irrelevant. So while it is the correct type to use for numbers not exceeding 9999, it is also the correct type for numbers not exceeding 19999, for instance.

Secondly, the storage required for each type is given on the MySQL manual page describing the types . Larger types will certainly reserve more resources; whether they reserve too much is another matter.

The INT(4) syntax you referred to is a MySQL-specific feature discussed separately in the manual under Numeric Type Attributes . According to that page, it represents a "display width", in digits, constraining the minimum width when displaying values. It specifically states that "The display width does not constrain the range of values that can be stored in the column." so the storage allocated could not be adjusted downwards based on that hint.

Answer 2

Before answer your question Frank, let's take a look on the size of types:

tinyint: 1 byte, -128 to +127 / 0 to 255 (unsigned)
smallint: 2 bytes, -32,768 to +32,767 / 0 to 65,535 (unsigned)
mediumint: 3 bytes, -8,388,608 to 8,388,607 / 0 to 16,777,215 (unsigned)
int/integer: 4 bytes, -2,147,483,648 to +2,147,483,647 / 0 to 4,294,967,295 (unsigned)
bigint: 8 bytes, -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 / 0 to 18,446,744,073,709,551,615 (unsigned)

Every time you use INT(4), INT(3), INT(1) the number in the brackets is not about the storage, but how many you want to display/output. It is not related with the storage factor. Which means, 183542 is gonna still be kept as it is in a INT(2) field.