MySQL FullText search without FULLTEXT index

Within one of our systems we have an option that switches the search system between a LIKE search, or a FullText search with either IN BOOLEAN MODE or WITH QUERY EXPANSION For some rea开发者_开发技巧son, the FULLTEXT index was missing but when the system was set to be IN BOOLEAN MODE the query still worked, in the case of WITH QUERY EXPANSION the query failed with:

1191 - Can't find FULLTEXT index matching the column list

I'm a little confused here as these are both FULLTEXT searches but one seems to work without the Index even existing!.

Am i missing something?

FYI this is using MySQL 5

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Argh, just found the answer in the MySQL docs.

With regard to searches IN BOOLEAN MODE..

They can work even without a FULLTEXT index, although a search executed in this fashion would be quite slow.