6-12 varchar and char enum types enum Set set

1 character types Char and varchar

#官网: https://Dev.mysql.com/Doc/Refman/5.7/En/Char. html# Note: The parameters in char and varchar brackets refer to the length of the character #char type: fixed length, simple rough, wasted space, fast access speed range of characters:0-255(a Chinese is a character that is a UTF8 encoded 3 bytes) Store: When a value of type char is stored, a space is padded to the right to satisfy the length, for example: Specify a length of 10, save>10 characters error, save<10 characters are padded with spaces until 10 characters are stored for retrieval: When retrieving or saying a query, the results are automatically deleted trailing blanks unless we open pad_char_to_full_length SQL mode (set SQL mode:SETSql_mode= 'Pad_char_to_full_length'; Query the default mode for SQL:Select @ @sql_mode;) #varchar类型: variable length, precision, space saving, slow access speed range of characters:0-65535(If greater than 21845 will prompt for other types.) MySQL row maximum limit is 65535 bytes, character encoding is UTF-8: https://Dev.mysql.com/Doc/Refman/5.7/En/column-Count-limit.html) Storage: The varchar type stores the actual contents of the data, does not fill with spaces, if'AB', the trailing spaces will be saved. Emphasize: varchar type will add 1 before real data-A prefix of 2Bytes that is used to represent the number of bytes bytes of real data (1-2Bytes Maximum represents 65,535 digits, exactly as MySQL has a maximum byte limit on row, which is sufficient to use if the actual data<255bytes requires a 1Bytes prefix (1Bytes=8bit 2**8 The maximum representation of the number is 255) if the real data>255bytes requires a 2Bytes prefix (2Bytes=16bit 2**16 The maximum representation of the number is 65535) search: The trailing space will be saved, in the search or query, will also display the contents of the text, including spaces

You can use these two functions to verify:

Length (): View number of bytes char_length (): View characters

Summarize

#常用字符串系列: char vs. varchar NOTE: Although varchar is more flexible to use, the char data type is processed faster and sometimes exceeds the varchar processing speed from the overall system performance perspective%. Therefore, the user should design the database in a comprehensive consideration of various factors in order to achieve the best balance # Other string series (efficiency:Char>varchar>text) Text Series TinytextTEXTmediumtext Longtextblob Series Tinyblob BLOB mediumblob longblob binary seriesBINARY VARBINARYtext: The text data type is used to hold large, variable-length strings that can be set up to 65535 (2** -?1) characters. Mediumtext:aTEXT column  withA maximum length of  -,777,215(2** -?1) characters.longtext:aTEXT column  withA maximum length of 4,294,967,295 or4GB (2** +?1) characters.

2, enumeration types and collections

The value of a field can be selected only in a given range, such as a radio box, a multi-marquee

The enum radio can only select a value within a given range, such as gender sex sex male male/female female

Set multiple selection You can select one or more values within a given range (hobby 1, hobby 2, hobby 3 ...) ）

Mysql> Create TableConsumer ( -Idint,     -Namevarchar( -),     -Sex enum ('male','female',' Other'),     -  LevelEnum'Vip1','VIP2','VIP3','VIP4'), #在指定范围内, choose one more -FavSet('Play','Music','Read','study') #在指定范围内, Multi-Select - ); Query OK,0Rows Affected (0.03sec) MySQL> Insert  intoConsumerValues     -(1,'Zhao Yun','male','VIP2','Read,study'),     -(2,'Zhao Yun 2',' Other','VIP4','Play'); Query OK,2Rows Affected (0.00sec) Records:2Duplicates:0Warnings:0MySQL> Select *  fromconsumer;+------+---------+-------+-------+------------+|Id|Name|Sex|  Level |Fav|+------+---------+-------+-------+------------+|    1 |Zhao Yun|Male|Vip2| Read, study||    2 |Zhao Yun 2|Other|Vip4|Play|+------+---------+-------+-------+------------+Rowsinch Set(0.00Sec

6-12 varchar and char enum types enum Set set