mysql data types include: 1. Numeric type; 2. Date and time type; 3. String types are CHAR, VARCHAR, BINARY [binary data type], BLOB, TEXT [text type], ENUM [ Enumeration type] and SET [data collection].
mysql data types are:
The data types supported by MySQL are in several categories: Numeric types, date and time types and string (character) types.
Data type:
Note:
We often use num int when defining fields (10) In this way of writing unsigned, the int(10) does not mean that the field will store 10-length numbers.
int(M) represents the format of number display, and is only valid when the field attribute is set to zerofill.
eg:
Tinyint(4) -- The actual stored value is 2. If zerofill is not specified, the result of the query is 2. If zerofill is specified, then The query result is 0002, and 0 is used to fill the left side;
zerofill attribute:
If the field specifies the zerofill attribute, mysql will automatically Field plus UNSIGNED attribute.
The ZEROFILL attribute is ignored when involved in column expressions or UNION queries
Floating point:
Float(M,D): M is the number of digits in the number, including the integer part and decimal part; D is The decimal part ,[D If equal, the integer part is 0, and the maximum value is 0.99
eg:
Float(2,1) -- represents one integer and one decimal, eg:1.1
- ## Float(1,2) --
Syntax error, only 1 digits How can there be 2 decimal places
## About the default value:
- The default value must be a constant light, not a function or expression. Exception: The default value of
- TIMESTAMP
can be used CURRENT_TIMESTAMP
##BLOB and TEXT Cannot set default value -
If a column does not clearly indicate the default value:
- strict mode
-
mode, an error will be reported
If the mode is not in strict mode mode, the system will confirm the use according to the type What default value
Date and time format:
The date and time type representing time value is datetime (DATATIME) , date (DATA), timestamp (TIMESTAMP), time (TIME) and year (YEAR).
DATATIME range:
'1000-01-01 00:00:00'
'9999-12-31 23 :59:59'.
DATA range:
'1000-01-01'
'9999-12-31' TIMESTAMP range:
'1970-01-01 00:00:01'
'2038-01-19 03:14:07' TIME range :
'-838:59:59'
'838:59:59'
YEAR range: year(4) --- 1901~2155; year(2) --- 00~99
TIMESTAMP: The timestamp column is displayed in the same format as the DATETIME column. In other words, the display width is fixed to 19 characters and the format is 'YYYY-MM-DD HH:MM:SS'.
The TIMESTAMP data type provides automatic initialization and update. But there can only be one column with default value and update specified as CURRENT_TIMESTAMP
1. Automatic initialization and automatic update eg: ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
2. Only automatic initialization; eg: ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP
3. Only automatic update; eg: ts TIMESTAMP DEFAULT 0 ON UPDATE CURRENT_TIMESTAMP
4. None; eg: ts TIMESTAMP DEFAULT 0
String type :
The string types are CHAR, VARCHAR, BINARY [binary data type], BLOB, TEXT [text type], ENUM [enumeration type] and SET [data collection].
The difference between char and varchar: the difference in storage length lies in the maximum length and whether to retain spaces;
Char will retain spaces, varchar will not retain spaces
char is 0~255; varchar is 0~65535
## ENUM: An enumeration is a string object that selects a value from a list that explicitly enumerates the allowed values for the column specification when creating the table. [When the inserted value cannot match the value of the list, the default is the maximum index value]
, ,
numbers ENUM('0','1','2')
mysql> INSERT INTO t (numbers) VALUES(2),('2'),('3');mysql> SELECT * FROM t;+---------+ | numbers | +---------+ | 1 | | 2 | | 2 | +---------+
SET: A set is an object that can have zero or more value strings, each of which must be selected from a list to allow the value specified when creating the table. [When the inserted value cannot match the value of the list, MYSQL will ignore the value that does not exist in the list]
1 CREATE TABLE myset (col SET('a', 'b', 'c', 'd'));2 3 INSERT INTO myset (col) VALUES ('a,d'), ('d,a'), ('a,d,a'), ('a,d,d'), ('d,a,d');
It can be seen from the definition of ENUM The difference from SET is whether the value is one or more of the values specified when defining. There is also a different behavior when the inserted value does not exist in the list.
More related free learning recommendations: mysql tutorial(Video)
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