Chris Sansom wrote:
I'm sure there must be an accepted technique for this, but it's
something I haven't tried before, so if anyone can point me in the right
direction I'd be grateful.
I'm writing a search facility for a site where the data is stored in
several tables - let's say 5 for this example - and I want to order my
results according to where (if anywhere) matches are found. So...
Let's say I have tables 'speakers', 'topics', 'speakers_topics',
'articles', 'other'.
'speakers' is a table of speakers, with id, name and some text fields.
'topics' is a list of topics they address
'speakers_topics' relates the above two by pairs of id numbers
'articles' and 'other' are further tables of text data with possibly
more than one row for some speakers, identified by id.
I want to search the data in the following order:
name from 'speakers'
topics
text data from 'speakers'
text data from 'articles' and 'other'
...and order the results according to where in that hierarchy a match is
found.
So, if the user's search term matches one speaker's name field,
another's topic and someone else's text data, that's the order in which
the results should be ordered. Also, if the same person is matched from,
say, both name and text fields (which is very likely, as their name will
almost certainly appear in some of the text), the name should take
precedence in the ordering.
To complicate matters further, I'd like if possible to extend this to an
and/or situation. If the user enters two or more words, any results that
match all the words should be ordered above those that match only some
of the words.
I can probably do this relatively easily with a series of separate
queries (I'm doing all this from PHP, by the way), but that strikes me
as inefficient. Can it all be done in one big query, perhaps with
subqueries?
I've built similar systems with a series of UNION queries. Each UNION
has a column for "relevance", which can be a sum of CASE statements,
such as
IF(<name matches>, 1, 0) + IF(<text matches>, 1, 0) AS relevance...
The entire UNION can then be ordered by relevance. You could also just
add in an arbitrary number in each UNION, to get the effect of ordering
by where in the hierarchy the match is found.
Baron
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