Raimund Jacob wrote: > i am constructing a rather longish join where i want to > select distinct > rows only. however, i know that the join-rows i collect are distinct > within the first two columns (it's a primary key of one of the join > partners). many more columns are selected. > > question: can the optimizer tell how much of the query result to test > for distinctness ? can i help by providing the information to the > optimizer ?
Always the whole result will be tested for distinctness. There is no chance to tell 'only the first x columns plus column y and z should be checked' --> therefore no chance to provide this info to the optimizer. But, maybe I did not understand your explanation correctly, but you mean that you do have a result like this (without DISTINCT) c1 c2 c3 c4 --------------------- a b 1 2 a b 7 3 f s 2 4 and you want to say DISTINCTNESS for c1 and c2, no matter what the rest of the columns show? No, that must be a misunderstanding. Second try: if you know that two columns are distinct (the primary key) and you do have a 1 : 1 -join, then there is no need to say DISTINCT. Just an idea (without really catching the problem): could it be helpful to use a FROM-select with DISTINCT for one table before joining it with the other (depends on the join 1:1, 1:n, n:m)? Elke SAP Labs Berlin _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
