MySql `MATCH AGAINST` and `LIKE` combination to search for special characters

For example, in database i have row with phrase DN-NP. In input field i type DN- and want to find the row. Here is example http://sqlfiddle.com/#!9/f9235a/4 Tried to use FULLTEXT index and MATCH AGAINST

SELECT `name` 
FROM `domains` 
WHERE MATCH (`name`) AGAINST ('DN*' IN BOOLEAN MODE);

get no results.

Here https://dba.stackexchange.com/a/111895/55397 is advice to combine with LIKE. At the moment idea is in php something like

if( strlen($_POST['input_field_value']) <= 2 ){ 
$sql = 'SELECT `name` 
FROM `domains` 
WHERE MATCH (`name`) AGAINST ('DN*' IN BOOLEAN MODE)
OR `name` LIKE "%DN%"'; 
}

But LIKE "% %" too slow? Any ideas how to solve the problem (to find phrases that contains special characters)?

What about LOCATE (performance)?

SELECT name AS name7 
FROM domains 
WHERE LOCATE('DN',`name`)>0;

Solution

Indexes can help with speed by limiting the number of rows to look at. Most code shown so far requires testing every row.

FULLTEXT is very good at finding rows when its rules apply. I doubt if +DN* applies due to word-length and existence of punctuation.
`LIKE "DN-NP%" can use an index very efficiently. But that only works for the string being at the start of the column.
`LIKE "%DN-NP%" -- The leading wildcard requires checking every row.
LOCATE and any other string operator -- not sargable, so needs to look at every row.
REGEXP "DN-NP" -- slower than LIKE. (There are other situations where REGEXPcan be faster and/orLIKE` won't apply.)

If you have the min word-length set to 2, then this trick may be the most efficient:

WHERE MATCH(col) AGAINST("+DN +NP" IN BOOLEAN MODE)
  AND col LIKE '%DN-NP%'

The MATCH will efficiently whittle down the number of rows; the LIKE will make further whittle down the number or rows, but only looking at the small number from the MATCH.

Caveat: Which of these do you need to match or not match?:

abc DN-NP def
abc DNs-NPed def   -- look likes "plural", etc which FULLTEXT matches
abc DN-NPQRS def   -- word boundary issue
abc ZYXDN-NP def

REGEXP can match a "word boundary"; LIKE does not have such.

Please build a list of things you want to match / not match. We might have a better answer for you.