上面3图是书中MySQL帮助的使用小节;
实测:
我用DATE_FORMAT(date,format)函数的时候经常会记不清格式化的字符是啥,这个时候我会去求助度娘,然后从零散的帖子里找一个合适的,测试一下可用,就拿来用了,但没法马上找到一个比较完整系统一点的帖子,从看此书本章节,可知使用MySQL的帮助功能很实用;

mysql> ? contents;
You asked for help about help category: "Contents"
For more information, type 'help <item>', where <item> is one of the following
categories:
   Account Management
   Administration
   Components
   Compound Statements
   Contents
   Data Definition
   Data Manipulation
   Data Types
   Functions
   Geographic Features
   Help Metadata
   Language Structure
   Loadable Functions
   Plugins
   Prepared Statements
   Replication Statements
   Storage Engines
   Table Maintenance
   Transactions
   Utility

mysql> help Functions
You asked for help about help category: "Functions"
For more information, type 'help <item>', where <item> is one of the following
categories:
   Aggregate Functions and Modifiers
   Bit Functions
   Cast Functions and Operators
   Comparison Operators
   Date and Time Functions
   Encryption Functions
   Enterprise Encryption Functions
   Flow Control Functions
   GROUP BY Functions and Modifiers
   GTID
   Information Functions
   Internal Functions
   Locking Functions
   Logical Operators
   Miscellaneous Functions
   Numeric Functions
   Performance Schema Functions
   Spatial Functions
   String Functions
   Window Functions
   XML

mysql> help Date and Time Functions
You asked for help about help category: "Date and Time Functions"
For more information, type 'help <item>', where <item> is one of the following
topics:
   ADDDATE
   ADDTIME
   CONVERT_TZ
   CURDATE
   CURRENT_DATE
   CURRENT_TIME
   CURRENT_TIMESTAMP
   CURTIME
   DATE FUNCTION
   DATEDIFF
   DATE_ADD
   DATE_FORMAT
   DATE_SUB
   DAY
   DAYNAME
   DAYOFMONTH
   DAYOFWEEK
   DAYOFYEAR
   EXTRACT
   FROM_DAYS
   FROM_UNIXTIME
   GET_FORMAT
   HOUR
   LAST_DAY
   LOCALTIME
   LOCALTIMESTAMP
   MAKEDATE
   MAKETIME
   MICROSECOND
   MINUTE
   MONTH
   MONTHNAME
   NOW
   PERIOD_ADD
   PERIOD_DIFF
   QUARTER
   SECOND
   SEC_TO_TIME
   STR_TO_DATE
   SUBDATE
   SUBTIME
   SYSDATE
   TIME FUNCTION
   TIMEDIFF
   TIMESTAMP FUNCTION
   TIMESTAMPADD
   TIMESTAMPDIFF
   TIME_FORMAT
   TIME_TO_SEC
   TO_DAYS
   TO_SECONDS
   UNIX_TIMESTAMP
   UTC_DATE
   UTC_TIME
   UTC_TIMESTAMP
   WEEK
   WEEKDAY
   WEEKOFYEAR
   YEAR
   YEARWEEK

mysql> help DATE_FORMAT
Name: 'DATE_FORMAT'
Description:
Syntax:
DATE_FORMAT(date,format)

Formats the date value according to the format string. If either
argument is NULL, the function returns NULL.

URL: https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html

Examples:
mysql> SELECT DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y');
        -> 'Sunday October 2009'
mysql> SELECT DATE_FORMAT('2007-10-04 22:23:00', '%H:%i:%s');
        -> '22:23:00'
mysql> SELECT DATE_FORMAT('1900-10-04 22:23:00',
    ->                 '%D %y %a %d %m %b %j');
        -> '4th 00 Thu 04 10 Oct 277'
mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00',
    ->                 '%H %k %I %r %T %S %w');
        -> '22 22 10 10:23:00 PM 22:23:00 00 6'
mysql> SELECT DATE_FORMAT('1999-01-01', '%X %V');
        -> '1998 52'
mysql> SELECT DATE_FORMAT('2006-06-00', '%d');
        -> '00'

mysql>

顺着给出的URL,可用查看官方网站的文档:
URL: https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html

在官方文档的这个位置就有我想要的格式化的字符了:
https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html#function_date-format

MySQL格式化字符的表格