Hi all. Maybe mine is a stupid question, but I'd like to know the answer if possible. In an inner join involving a 16M+ rows table and a 100+ rows table performances got drastically improved by 100+ times by replacing a UNIQUE-NOT NULL index with a PRIMARY KEY on the very same columns in the very same order. The query has not been modified. In the older case, thanks to the EXPLAIN command, I saw that the join was causing a sort on the index elements, while the primary key was not. So ther's some difference for sure, but I'm missing it. Any hint? -- Vincenzo Romano -- Maybe Computer will never become as intelligent as Humans. For sure they won't ever become so stupid. [VR-1988]
