Is signed or unsigned selected to create an integer field in MySQL? The answer is as follows:

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The symbol is “+” Plus sign and “-” minus sign ,+ No. is omitted , Positive numbers are stored in the database table , The default is not to display “+” Number , If you save a negative number , Then it will show “-” Number .
Each type of integer is unsigned （unsigned） And signed （signed） Two types of （float and double Always signed ）, By default, declared integer variables are signed types （char A little special ）, If you want to declare an unsigned type, you need to add... Before the type unsigned.

The difference between unsigned and signed versions is that unsigned types can save 2 Times positive integer data of signed type , such as 16 One of the bit systems smallint The range of data that can be stored is -32768~32767, and unsigned The range of data that can be stored is 0~65535.

Because in the computer , Integers are stored as complements . According to the highest order , If it is 1, A signed number is a negative number ; If it's an unsigned number , Are interpreted as positive numbers .

in addition ,unsigned If you omit the last keyword , Most compilers will think of it as unsigned int.

In short, because Int Type occupation 4 byte , That is to say 16 position ,2^16 = 65535, If there are sign bits + - Equally divided on both sides , If not, give it all +.