MySQL three major column types

MySQL three major column types

Numeric type

Integral type: Tinyint

1 of bytes 8 Digit bit Storage Range 0---2^8-(0--255)

0000 0000 =0

1111 1111 =2^8-1=255

The computer in order to indicate a number is negative, will be the highest bit ( left ) of the 0/1, when fit to see

if the 0 is a positive number, if 1 , it is a negative number

0 0000000 0 1111111–>0->127

1 0000000 à -0 1 1111111 à -127

The question of twos complement

understand as above +0 and the -0 , the possibility of wasting a storage is repeated.

so the computer kind of negative, not according to "the absolute value of the back directly multiplied -1 get the "

Negative number = absolute value-128

So

1111 1111----. >-1

0000--- à -128

Smallint

Mediuint

Int

Bigint

Analysis:

2 bytes, - bit 0-----2^16-1=65535

-2^15-- à +2^15-1, -32768--- à 32767

in general, set a type N of bytes

N bytes, 8N bit.

0------ à 2^8n-1

-2^ (8n-1)--- à +2^ (8n-1);

for int Type: The more bytes that are occupied, the greater the range of storage

Int parameters for the declaration of the series:

( M ) unsigned zerofil

Learning tinyint parameters and verify the relationship of the byte to the range

Out of range out of range

that int without special instructions, the default is to comply with

# Plus unsigned represents unsigned, can affect the range of storage

# Plus unsigned type denotes unsigned

# Analysis M Parameters

#zerofill Zero is a 0 ; Fill Fill,

#M must and Zerofill cooperation is interesting, not enough digits, with 0 Fill

why add to 5 bit, because M to be 5 bit, so M with the Zerofill It's fun to work with.

decimal (floating-point / fixed-point type)

Floating-point numbers are more complex to represent in a computer.

Float ( m,d ) decimal ( m,d )

M called Precision ---- à represents the total number of decimal places, and D is the scale, representing the decimal place (the number of digits to the right of the decimal point)

Float(6,2) range -9999.99-------+9999.99

MySQL three major column types