Hello, On Fri, Nov 19, 2010 at 01:03:14PM +0100, Wolfgang Rohdewald wrote: > On Freitag 19 November 2010, Alexander Gattin wrote: > > It's better to select count(1) instead of > > count(*).
not true, > > The latter may skip rows consisting > > entirely of NULLs IIRC. not true either. I've heard that count(1) is preferred to count(*) but forgot why. Your post reveals the truth about my belief: > in some data bases count(1) is said to be faster > than count(*), I believe And as it turns out this isn't true anymore on modern databases (count(1) and count(*) behave exactly the same). And quite surprisingly, on old ones count(*) was faster than count(1): > 'Oracle Performance Tuning', second edition, > O'Reilly & Associates, Inc, page 175. It says: > > "Contrary to popular belief COUNT(*) is faster > than COUNT(1). If the rows are returned via an > index, counting the indexed column - for example, > COUNT(EMP_NO) is faster still. The optimizer > realizes from the existence of the index that the > column must also exist (non-null). We tested the > following statements on several different > computers and found that COUNT(*) consistently > runs between 15% and 20% faster than COUNT(1) and > that COUNT(INDEXED_COLUMN) is 5% faster again." // http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1156151916789 P.S. sorry for starting this discussion. -- With best regards, xrgtn -- http://mail.python.org/mailman/listinfo/python-list
