insert into client (username,country) values ('صیdf2بdfdلت', 'per'); 

insert into client (username, country) values ('ㄷㅅdfㅅㅅ89ㅎㅎ', 'korean'); 
insert into client (username, country) values ('ğĞGÇç24ööFc', 'azerb'); 
insert into client(username, country) values ('DhËFGjJopq', 'albany');

select * from client c where (c.username ~* '(?:[a-zA-Z]\d)|(?:\d[a-zA-Z])') is false;

• *'：alnum：'**-在这种情况下，此表达式将找不到必需的字符串

/*
This expression searches for all strings that are not in the Unicode range:
48 - 57 - digits
65 - 90 - uppercase letters
97 - 122 - lowercase letters

~*    case-insensitive matches

^  $  set at the beginning and at the end, indicate the exact definition of the condition

+    quantifier, indicates that there can be any number of characters that a string has.
*/

select * from login l where (l.username ~* '^[A-Za-z0-9]+$') is false;