[Database] learn basic SQL data types

Numeric types

Exact type

type of data	Use storage	Explanation
bit	First place	Keep only 0 or 1
tinyint	1 byte	Range 0 to 255
smallint	2 bytes	Range of -2 15 to 2 15 -1, i.e. -32768 to 32767
int	4 bytes	Range of -2 31 is to 2 31 is -1, i.e., 2,147,483,648 - 2,147,483,647
bigint	8 bytes	Range of -2 63 is to 2 63 is -1
decimal(p,s)	And related precision	p represents the number of decimal places and the left and right, s represents the number of digits to the right of the decimal point, p ranges from 1 to 38, default is 18. S ranges from 0 to p, the default is 0
numeric(p,s)	And related precision	p represents the number of decimal places and the left and right, s represents the number of digits to the right of the decimal point, p ranges from 1 to 38, default is 18. S ranges from 0 to p, the default is 0
smallmoney	4 bytes	Maximum 214748.3647
money	8 bytes	922,337,203,685,477.5808 maximum value, this value is actually 2 63 is -1 to move the decimal point to give

Approximation type

type of data	Use storage	Explanation
float(n)	Depending on n	n is the number of bits of the mantissa values stored float, n ranges from 1 to 53, the default value is 53. SQL Server, if n is between 1 and 24, n regarded as 24, n 25 to 53, 53 n regarded. When the value of n is 24, 4 bytes. The value of n is 53, 8 bytes. Range divided into three sections, $-1.79 \ times10 ^ {308} to -2.23 \ times10 ^ {- 308}, 0,2.23 \ times10 ^ {- 308} to 1.79 \ times10 ^ {308}$
real	4 bytes	Range divided into three sections, $-3.40 \ times10 ^ {38} to -1.18 \ times10 ^ {- 38}$，0， $1.18 \ times10 ^ {- 38} to 3.40 \ times10 ^ {38}$

Text Types

Ordinary character encoding

Each English character occupies one byte, two bytes for each character

type of data	Use storage	Explanation
char(n)	n bytes	Fixed length, n ranges from 1 to 8000
varchar(n)	Data storage and related storage of an English characters occupy one byte	Variable length, n represents the maximum length of the string stored, n ranges from 1 to 8000
text	And storing data related to store a two-byte characters representing	Variable-length string maximum length of 2 31 is -1 bytes

Unicode character encoding

Each character in English and Chinese characters are two bytes

type of data	Use storage	Explanation
nchar(n)	n bytes	Fixed length, n ranges from 1 to 4000
nvarchar(n)	Data storage and related storage of an English characters occupy two bytes	Variable length, n represents the maximum length of the string stored, n ranges from 1 to 4000
ntext	And storing data related to store a two-byte characters representing	Variable-length string maximum length of 2 30 -1 or kanji characters

Date Time Type

type of data	Use storage	Explanation
data	3 byte	Range 0001/01/01 to 9999/12/31
time	5 bytes	Range 00:00: 00.0000000 to 23: 59: 59.9999999
datetime	8 bytes	1753/01/01/00 range: 00:00 to 9999/12/31/23: 59: 59: 997
smalldate	4 bytes	1900/01/01/00 range: 00:00 to 2079/06/06/23: 59: 59

Binary type

type of data	Use storage	Explanation
binary(n)	n bytes	Fixed-length binary data, n ranges from 1 to 8000
varbinary(n)	And related data stored	Variable-length binary data, n represents the maximum storage bytes, n ranges from 1 to 8000
image	And related data stored	长度可变的二进制数据，存储的最大值是231-1个字节，约等于2GB
varbinary(max)	与存放的数据有关	代替image