There are two kinds of numbers: whole numbers and real numbers (numbers with afractional part). If you’re storing whole numbers, use one of the integer types: TINYINT, SMALLINT, MEDIUMINT, INT, or BIGINT. These require 8, 16, 24, 32, and 64 bits of storage space, respectively. They can store values from −2(N–1) to 2(N–1)–1, where N is the numberof bits of storage space they use.
Integer types can optionally have the UNSIGNED attribute, which disallows negative values and approximately doubles the upper limit of positive values you can store. For example, a TINYINT UNSIGNED can store values ranging from 0 to 255 instead of from−128 to 127.
Signed and unsigned types use the same amount of storage space and have the same performance, so use whatever’s best for your data range.Your choice determines how MySQL stores the data, in memory and on disk. However, integer computations generally use 64-bit BIGINT integers, even on 32-bit architectures.(The exceptions are some aggregate functions, which use DECIMAL or DOUBLE to performcomputations.).
MySQL lets you specify a “width” for integer types, such as INT(11). This is meaningless for most applications: it does not restrict the legal range of values, but simply specifiesthe number of characters MySQL’s interactive tools (such as the command-line client) will reserve for display purposes. For storage and computational purposes, INT(1) isidentical to INT(20).
原文：http://www.cnblogs.com/yuanjiangw/p/5838434.html