MySQL Data type analysis

CHAR, VARCHAR, TEXT

• CHAR fixed length string, high space, fast
• VARCHAR variable length string, small footprint, slow speed
• The space behind the char is removed, and varchar does not remove
• TEXT cannot have a default value
• Efficiency of data Retrieval CHAR > VARCHAR > TEXT

ENUM ()

• Each element of an enumeration has an ordinal number
• Automatically remove the space behind the element
• Value must be one of the enumerations when inserting data, except NULL
• Only one value can be selected from the list

SET ()

• You can select more than one value from the list, and multiple values are separated by commas
• Save in a table with a binary value

Year:

• Year saved 1901-2155
• You can save the numeric form, or you can save the string form
• When you enter a two-digit or two-bit string, the prefix is automatically preceded by 20 or 19.
• When inserting a number 0 o'clock, save to 0000
• When inserting a string 0 o'clock, save to 2000

Time:

• By days: Hours: minutes: seconds
• INSERT tablename VALUES (' 1 12:12:12 '); Save into 36:12:12
• INSERT tablename VALUES (' 11:11 '); Save into 11:11:00
• INSERT tablename VALUES (' 1234 '); Save into 00:12:34
• INSERT tablename VALUES (' 12 '); Save into 00:00:12
• INSERT tablename VALUES (' 0 '); Save into 00:00:00

DATE:

• 1000-0101 ~ 9999-12-31
• INSERT tablename VALUES (' 12-6-7 '); 2012-06-07
• INSERT tablename VALUES (' 12/6/7 '); 2012-06-07
• INSERT tablename VALUES (' 120607 '); 2012-06-07
• INSERT tablename VALUES ('[email protected]/7 '); 2012-06-07
• General time save timestamp with integer type

Floating-point types:

• When inserting data in decimal place too many, float, double will automatically round; Decimal produces a warning.
• Inside decimal is saved as a string
• When a value is inserted as a string, float, double saves the result may be incorrect, but the decimal is not wrong
• When the accuracy requirement is high, you should use decimal

MySQL Data type analysis