SQL is used for field data types in various databases

Microsoft Access、MySQL and SQL Server The type and range of data used .

Microsoft Access data type

data type	describe	Storage
Text	For text or a combination of text and numbers .	most 255 Characters .
Memo	Memo For a larger number of texts . Maximum storage 65,536 Characters . notes ： Be able to memo Field to sort . But they are searchable .
Memo	Memo For a larger number of texts . Maximum storage 65,536 Characters . notes ： Be able to memo Field to sort . But they are searchable .
Byte	allow 0 To 255 The number of .	1 byte
Integer	Allow between -32,768 And 32,767 All the numbers between .	2 byte
Long	Allow between -2,147,483,648 And 2,147,483,647 All the numbers between .	4 byte
Single	Single precision floating point . Handle most decimals .	4 byte
Double	Double precision floating point . Handle most decimals .	8 byte
Currency	For money . Support 15 Bitwise element , Plus 4 Decimal place . Tips ： You can choose which currency to use .	8 byte
AutoNumber	AutoNumber Fields automatically assign numbers to each record , Usually from 1 Start .	4 byte
Date/Time	For date and time	8 byte
Yes/No	Logical fields , It can be shown as Yes/No、True/False or On/Off. In the code , Use a constant True and False ( Equivalent to 1 and 0). notes ：Yes/No The... Is not allowed in the field Null value	1 The bit
Ole Object	Can store pictures 、 Audio 、 Video or something BLOBs(Binary Large OBjects).	most 1GB
Hyperlink	Contains links to other files , Including web pages .
Lookup Wizard	Allows you to create a list of options that can be selected from the drop-down list .	4 byte

MySQL data type

stay MySQL in , There are three main types ：Text( Text )、Number( Numbers ) and Date/Time( date / Time ) type .

Text type ：

data type	describe
CHAR(size)	Saves a fixed length string ( Can contain letters 、 Numbers and special characters ). Specify the length of the string in parentheses . most 255 Characters .
VARCHAR(size)	Save variable length strings ( Can contain letters 、 Numbers and special characters ). Specify the maximum length of the string in parentheses . most 255 Characters . notes ： If the length of the value is greater than 255, Is converted to TEXT type .
TINYTEXT	The maximum storage length is 255 Character string .
TEXT	The maximum storage length is 65,535 Character string .
BLOB	be used for BLOBs(Binary Large OBjects). Store up to 65,535 Bytes of data .
MEDIUMTEXT	The maximum storage length is 16,777,215 Character string .
MEDIUMBLOB	be used for BLOBs(Binary Large OBjects). Store up to 16,777,215 Bytes of data .
LONGTEXT	The maximum storage length is 4,294,967,295 Character string .
LONGBLOB	be used for BLOBs (Binary Large OBjects). Store up to 4,294,967,295 Bytes of data .
ENUM(x,y,z,etc.)	Allows you to enter a list of possible values . Can be in ENUM List the largest 65535 It's worth . If there is no inserted value in the list , Then insert a null value . notes ： The values are sorted in the order you enter . You can enter the possible values in this format ： ENUM('X','Y','Z')
SET	And ENUM similar , The difference is ,SET It can only contain at most 64 List items and SET Can store more than one choice .

Number type ：

data type	describe
TINYINT(size)	Signed -128 To 127 , Unsigned 0 To 255.
SMALLINT(size)	Signed range -32768 To 32767, Unsigned 0 To 65535, size The default is 6.
MEDIUMINT(size)	Signed range -8388608 To 8388607, The unsigned range is 0 To 16777215. size The default is 9
INT(size)	Signed range -2147483648 To 2147483647, The unsigned range is 0 To 4294967295. size The default is 11
BIGINT(size)	The signed range is -9223372036854775808 To 9223372036854775807, The unsigned range is 0 To 18446744073709551615.size The default is 20
FLOAT(size,d)	A small number with a floating decimal point . stay size The parameter specifies the maximum number of digits to be displayed . stay d The parameter specifies the maximum number of digits to the right of the decimal point .
DOUBLE(size,d)	A large number with a floating decimal point . stay size The parameter shows the fixed maximum number of digits . stay d The parameter specifies the maximum number of digits to the right of the decimal point .
DECIMAL(size,d)	Stored as a string DOUBLE type , Allow fixed decimal point . stay size The parameter specifies the maximum number of digits to be displayed . stay d The parameter specifies the maximum number of digits to the right of the decimal point .

 Be careful ： The above  size  It doesn't represent the specific length stored in the database , Such as  int(4)  It's not just storage 4 A number of lengths .

 actually int(size) It doesn't matter how much storage space it takes .int(3)、int(4)、int(8)  It's all on disk  4 btyes  Storage space . It's just that the way it's displayed to users is a little different ,int(M)  Follow  int  The data type is the same .

 for example ：

1、int The value of is 10 ( Appoint zerofill)

int(9) The result is 000000010
int(3) The result is 010
 It's just that the length of the display is not the same   All take up four bytes of space 

Date type ：

data type	describe
DATE()	date . Format ：YYYY-MM-DD notes ： The scope of support is from '1000-01-01' To '9999-12-31'
DATETIME()	* A combination of date and time . Format ：YYYY-MM-DD HH:MM:SS notes ： The scope of support is from '1000-01-01 00:00:00' To '9999-12-31 23:59:59'
TIMESTAMP()	* Time stamp .TIMESTAMP Value usage Unix An era ('1970-01-01 00:00:00' UTC) Seconds to date to store . Format ：YYYY-MM-DD HH:MM:SS notes ： The scope of support is from '1970-01-01 00:00:01' UTC To '2038-01-09 03:14:07' UTC
TIME()	Time . Format ：HH:MM:SS notes ： The scope of support is from '-838:59:59' To '838:59:59'
YEAR()	2 Bit or 4 Bit format year . notes ：4 Value allowed by bit format ：1901 To 2155.2 Value allowed by bit format ：70 To 69, From 1970 To 2069.

* Even if DATETIME and TIMESTAMP Return the same format , They work in very different ways . stay INSERT or UPDATE Querying ,TIMESTAMP Automatically set itself to the current date and time .TIMESTAMP Also accept different formats , such as YYYYMMDDHHMMSS、YYMMDDHHMMSS、YYYYMMDD or YYMMDD.

SQL Server data type

String type ：

data type	describe	Storage
char(n)	Fixed length string . most 8,000 Characters .	Defined width
varchar(n)	Variable length string . most 8,000 Characters .	2 bytes + number of chars
varchar(max)	Variable length string . most 1,073,741,824 Characters .	2 bytes + number of chars
text	Variable length string . most 2GB Text data .	4 bytes + number of chars
nchar	Fixed length Unicode character string . most 4,000 Characters .	Defined width x 2
nvarchar	Variable length Unicode character string . most 4,000 Characters .
nvarchar(max)	Variable length Unicode character string . most 536,870,912 Characters .
ntext	Variable length Unicode character string . most 2GB Text data .
bit	allow 0、1 or NULL
binary(n)	Fixed length binary string . most 8,000 byte .
varbinary	Variable length binary string . most 8,000 byte .
varbinary(max)	Variable length binary string . most 2GB.
image	Variable length binary string . most 2GB.

Number type ：

data type	describe	Storage
tinyint	Allow from 0 To 255 All the numbers of .	1 byte
smallint	Allow between -32,768 And 32,767 All the numbers of .	2 byte
int	Allow between -2,147,483,648 And 2,147,483,647 All the numbers of .	4 byte
bigint	Allow between -9,223,372,036,854,775,808 And 9,223,372,036,854,775,807 All numbers between .	8 byte
decimal(p,s)	Fixed precision and scale figures .</br> Allow from -10^38 +1 To 10^38 -1 Number between .</br>p Parameter indicates the maximum number of bits that can be stored ( To the left and right of the decimal point ).p Must be 1 To 38 Between the value of the . The default is 18.</br>s Parameter indicates the maximum number of digits stored to the right of the decimal point .s Must be 0 To p Between the value of the . The default is 0.	5-17 byte
numeric(p,s)	Fixed precision and scale figures .</br> Allow from -10^38 +1 To 10^38 -1 Number between .</br>p Parameter indicates the maximum number of bits that can be stored ( To the left and right of the decimal point ).p Must be 1 To 38 Between the value of the . The default is 18.</br>s Parameter indicates the maximum number of digits stored to the right of the decimal point .s Must be 0 To p Between the value of the . The default is 0.		5-17 byte
smallmoney	Be situated between -214,748.3648 And 214,748.3647 Currency data between .	4 byte
money	Be situated between -922,337,203,685,477.5808 And 922,337,203,685,477.5807 Currency data between .	8 byte
float(n)	from -1.79E + 308 To 1.79E + 308 The floating precision of digital data .</br>n Parameter indicates that the field saves 4 Byte or 8 byte .float(24) preservation 4 byte , and float(53) preservation 8 byte .n The default value of is 53.	4 or 8 byte
real	from -3.40E + 38 To 3.40E + 38 The floating precision of digital data .	4 byte

Date type ：

data type	describe	Storage
datetime	from 1753 year 1 month 1 Japan To 9999 year 12 month 31 Japan , Accuracy of 3.33 millisecond .	8 byte
datetime2	from 1753 year 1 month 1 Japan To 9999 year 12 month 31 Japan , Accuracy of 100 nanosecond .	6-8 byte
smalldatetime	from 1900 year 1 month 1 Japan To 2079 year 6 month 6 Japan , Accuracy of 1 minute .	4 byte
date	Store date only . from 0001 year 1 month 1 Japan To 9999 year 12 month 31 Japan .	3 bytes
time	Storage time only . Accuracy of 100 nanosecond .	3-5 byte
datetimeoffset	And datetime2 identical , Plus time zone offset .	8-10 byte
timestamp	Store unique numbers , Whenever a line is created or modified , The number will be updated .timestamp Value based on internal clock , It doesn't correspond to the real time . Each watch can only have one timestamp Variable .

Other data types ：

data type	describe
sql_variant	Store the most 8,000 Byte data of different data types , except text、ntext as well as timestamp.
uniqueidentifier	Store globally unique identifier (GUID).
xml	Storage XML Format data . most 2GB.
cursor	Store references to pointers used for database operations .
table	Save the result set , For later processing .