MySQL commonly used data types and field attributes

type of data

Value

• tinyint Very small data 1 byte
• smallint 2 bytes for the smaller data
• mediumint Medium-sized data 3 bytes
• int Standard integer 4 bytes are commonly used
• bigint Larger data 8 bytes
• float Floating point number 4 bytes
• double Floating point 8 bytes
• decimal String floating point financial calculation

String

• char Fixed-size string 0~255
• varchar Variable string 0~65535 commonly used
• tinytext Micro text 2^8-1
• text Text string 2^16-1 save large text

Time and date

• date YYYY-MM-DD date format
• time HH: mm: ss time format
• datetime YYYY-MM-DD HH: mm: ss date and time format commonly used
• timestampThe total number of milliseconds from the timestamp 1970.1.1 to the present
• year years

null

• No value, unknown
• Do not use Null to perform operations, the result is null

Database field properties

Unsigned

• Unsigned integer
• Declared that the column cannot be negative

zerofill

• 0 padding
• Insufficient digits use 0 to fill int(3), 5 – 005

Self-increasing

• Automatically +1 on the basis of the previous record
• Usually used to set the unique primary key ~ index, must be an integer type
• You can set the starting value and

Null, not Null

• Assuming it is set to not Null, an error will be reported if the value is not filled
• null, if the value is not filled, the default is null

default

• Set the default value
• sex, the default value is male, if the column value is not specified, it will be filled with the default value