"Richard Huxton" <[EMAIL PROTECTED]> writes: > Now you and I can look at a substring and probably make a good guess how > common > it is (assuming we know the targets are British surnames or Japanese towns). > PG > needs one number - or rather, it picks one number for each length of > search-string (afaik).
I don't think that's true. Postgres calculates the lower and upper bound implied by the search pattern and then uses the histogram to estimate how selective that range is. It's sometimes surprisingly good but obviously it's not perfect. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
