为什么mysql十六进制结果与shell和java不同

Question

我想要获得汉字的Unicode字符表示，例如， '京' --> 4eac

Shell

➜ ~ printf "%x\n" \'京 
4eac 

Java

jshell> Integer.toHexString('京'); 
$14 ==> "4eac" 

为什么在MySQL中它有差异的结果？

select hex('京'); 
+------------+ 
| hex('京') | 
+------------+ 
| E4BAAC  | 
+------------+ 

show variables like 'char%'; 
+--------------------------+------------------------------------------------------+ 
| Variable_name   | Value            | 
+--------------------------+------------------------------------------------------+ 
| character_set_client  | utf8             | 
| character_set_connection | utf8             | 
| character_set_database | utf8             | 
| character_set_filesystem | binary            | 
| character_set_results | utf8             | 
| character_set_server  | utf8             | 
| character_set_system  | utf8             | 

在MySQL它必须使用以下方式来得到相同的结果如上

select hex(convert('京' using ucs2)); 
+--------------------------------+ 
| hex(convert('京' using ucs2)) | 
+--------------------------------+ 
| 4EAC       | 
+--------------------------------+ 

那么，为什么hex在MySQL中是不同与其他？

除了从Unicode字符

壳牌

➜ ~ echo '\u4eac' 
京 

爪哇

jshell> String s = "\u4eac"; 
s ==> "京" 

Mysql的

select char(0x4eac using ucs2); 
+-------------------------+ 
| char(0x4eac using ucs2) | 
+-------------------------+ 
| 京      | 
+-------------------------+ 

Answer 1

UTF-8（MySQL的UTF8或utf8mb4）是一个不同的编码比UCS2（MySQL：ucs2）。

'京' = 
Unicode "codepoint" (in hex) '4eac' = 
UCS2 encoding (2 bytes, in hex) '4EAC' = 
UTF-8 encoding (3 bytes, in hex) 'E4BAAC' = 
html entity '京' (hex) or '京' (decimal) 

参考：http://unicode.scarfboy.com/?s=U%2B4eac