Question

I have a mySQL wildcard query that isn’t working probably because I use InnoDB instead of MyISAM.

SELECT a.product_id, a.category_id FROM products a 
LEFT JOIN users u ON u.userid=a.ownerid 
WHERE a.active=1 AND a.approved=1 
AND a.deleted=0 AND a.name LIKE '%*my*%' 
AND a.name LIKE '%*donuts*%' 
AND (a.name REGEXP '( )*(*my*)*( )*(*donuts*)( )*') 

It works fine whenever a word is used instead of a wildcard, that’s not the problem.

I’m just wondering, is the part of

(a.name REGEXP '( )*(*my*)*( )*(*donuts*)( )*') 

really needed after already doing a

LIKE '%*my*%' AND a.name LIKE '%*donuts*%'

What is the difference?

Answer 1

What is the difference?

• The regular expression

  (a.name REGEXP '( )*(*my*)*( )*(*donuts*)( )*')
  

  This produces an error, because a quantifier (e.g. an unescaped * character) is not valid at the start of a group (i.e. immediately after an unescaped ( character). Ignoring the two times where that occurs yields:

  (a.name REGEXP '( )*(my*)*( )*(donuts*)( )*')
  

  This matches any a.name with:

  1. zero or more spaces, followed by

  2. zero or more occurrences of:

     • the letter m, followed by
     • zero or more letters y

     followed by

  3. zero or more spaces, followed by
  4. the character sequence donut, followed by
  5. zero or more letters s, followed by
  6. zero or more spaces

   

• The simple pattern

  a.name LIKE '%*my*%' AND a.name LIKE '%*donuts*%'
  

  This matches any a.name with:

  1. any sequence of characters, followed by
  2. the character sequence *my*, followed by
  3. any sequence of characters

  and with:

  4. any sequence of characters, followed by
  5. the character sequence *donuts*, followed by
  6. any sequence of characters