Optimizing MySQL LIKE '%string%' queries in innoDB

Question

Having this table:

CREATE TABLE `example` (
`id` int(11) unsigned NOT NULL auto_increment,
`keywords` varchar(200) NOT NULL,
PRIMARY KEY  (`id`)
) ENGINE=Inn         


        

Answer 1

I would like to comment that surprisingly, creating an index also helped speed up queries for like '%abc%' queries in my case.

Running MySQL 5.5.50 on Ubuntu (leaving everything on default), I have created a table with a lot of columns and inserted 100,000 dummy entries. In one column, I inserted completely random strings with 32 characters (i.e. they are all unique).

I ran some queries and then added an index on this column. A simple

select id, searchcolumn from table_x where searchcolumn like '%ABC%'

returns a result in ~2 seconds without the index and in 0.05 seconds with the index.

This does not fit the explanations above (and in many other posts). What could be the reason for that?

EDIT I have checked the EXPLAIN output. The output says rows is 100,000, but Extra info is "Using where; Using index". So somehow, the DBMS has to search all rows, but still is able to utilise the index?