Re: Vietnamese character matching with %LIKE%

[Rick James]

First, let's see what character set and collation you are using. Please do
SHOW CREATE TABLE tablename;

Second, let's verify what is in the table -- please do
SELECT name, HEX(name) FROM tablename WHERE ...
to show the internal representation of that string. See this for more discussion of this debugging technique:
http://mysql.rjweb.org/doc.php/charcoll

Third, I can discuss things in more detail after those. Including, we will talk about whether 'Đ' matches 'D' in the collation you are using. Possibly I will need to recommend a different character set and/or collation.