12/4/2023 0 Comments Mysql like vs substringSolution: Please do use the WHERE clause, and use EXPLAIN to see the performance. LIKE, ILIKE, and RLIKE all perform similar operations however, RLIKE uses POSIX EXE (Extended Regular Expression) syntax instead of the SQL pattern syntax used. Both scenario's:ġ/ If you do SELECT field FROM table WHERE field LIKE "%value%", MySQL will scan the entire table, and only send the fields containing "value".Ģ/ If you do SELECT field FROM table and then have your application (in your case PHP) filter only the rows with "value" in it, MySQL will also scan the entire table, but send all the fields to PHP, which then has to do additional work. I say that doing a WHERE field LIKE "%value%" is slower than WHERE field LIKE "value%" if the column field has an index, but this is still considerably faster than getting all values and having your application filter. In your case a firstname is more likely to be matched using LIKE than REGEXP and hence, it will be more optimized. This is an index where the keys are individual terms, and the associated values are sets of. Most full text search implementations use an 'inverted index'. A full text search facility gives you a lot of flexibility to tune down the precision for better recall. Also, the execution plan shows a recommended index for Method 2 that could improve its performance. LIKE is used to add wildcards to a string whereas REGEXP is used to match an attribute with Regular Expressions. Using the LIKE operator gives you 100 precision with no concessions for recall. Method 1: ON tB.columnB like tA.columnA '' Method 2: ON substr (tB.columnB,1,2) tA.columnA The query execution plan has a lot less steps using Method 1 compared to Method 2, however, it looks like Method 2 executes much faster. Updated answer to reflect question update: REGEXP and LIKE are used to totally different cases. By default, the search will be case-insensitive. Whether the search is case-sensitive or not depends on how you stock the data, especially what COLLATION you use. To get the columns that don't match, simply put a NOT in front of the like: WHERE textcolumn NOT LIKE "%SUBSTRING%". It depends on the field type - a textarea usually won't be saved as VARCHAR, but rather as (a kind of) TEXT field, so you can use the MATCH AGAINST operator. Well, you can always try WHERE textcolumn LIKE "%SUBSTRING%" - but this is guaranteed to be pretty slow, as your query can't do an index match because you are looking for characters on the left side.
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