3 Notes for MYSQL data types

Note 1,

Bit (length), the maximum length of this data type is only 64, which means

Bit (2) to

Bit (64) to

Bit (65) wrong

Bit (100) wrong

Note 2, serial

Serial is an alias of bigint UNSIGNED not NULL auto_increment unique.

Note 3,

tinyint (length) can only store -128~127,unsigned cases under 0~255 conditions. No matter what length you specify.

Note 4,

Unsigned when you do the subtraction,

Such as:

CREATE TABLE Nums (X int unsigned, Y int unsigned);

INSERT into Nums (x, Y) VALUES (100,200);

Select X-y from Nums;

This is not good because x = 100,y = 200; so xy =-100, but two unsigned data operation result also requires unsigned type, so error occurs

3 Notes for MYSQL data types