On Sun, 7 Apr 2002, [ISO-8859-1] Kjartan Ásþórsson wrote: > Is there any indexing technique available I can use when joining tables > with a regular expression pattern in pgsql? > > I know one method for indexing strings that will be matched with regular > expression patterns, and that is using so called k-gram indexes. > Indexing the string "kjartan" with k-gram index where k = 3 would > create "kja", "jar", "art", "rta", "tan" as an index. Ofcourse it is hard to
Usually, k-grams technique is used to match patterns with errors and 3-grams produce "__k", "_kj", "kja", "jar", "art", "rta", "ta_", "a__" where leading and trailing spaces are used to compensate 'boundary' effect. But I dont' quite understand your question. Are you looking for fuzzy match ? If so, take a look on contrib modules. > decide the size of k and I'm sure in many cases mulitple k values might > be needed, depending on the situation. > > I have not done any major survey of available techniques, but I was > hoping I could get some pointers here. > > I assume pgsql always uses nested loop join when joining relations which are > joined with regular expression pattern? > Regards, Oleg _____________________________________________________________ Oleg Bartunov, sci.researcher, hostmaster of AstroNet, Sternberg Astronomical Institute, Moscow University (Russia) Internet: [EMAIL PROTECTED], http://www.sai.msu.su/~megera/ phone: +007(095)939-16-83, +007(095)939-23-83 ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]