On Thu, 12 Sep 2002, Stephan Szabo wrote: > On Thu, 12 Sep 2002, Andrew Perrin wrote: > > > Greetings- > > > > I have a table of participants to be contacted for a study. Some are in > > the "exposure" group, others in the "control" group. This is designated by > > a column, typenr, that contains 1 for exposure, 2 for control. > > > > The complication is this: I need to select 200 total. The 200 number > > should include *all* those eligible in the exposure group, plus enough > > from the control group to bring the total number up to 200. (Yes, there is > > a valid reason for this.) Furthermore, I need to sort the output of the > > two groups *together* by zip code. > > Do you get more than 200 if there are more eligible people
Yes - in the (rather rare) case that there are 200 or more eligible exposure subjects, the result set should be the total number of eligible exposure subjects. > and does the > ... ever include the same person in both sides of the union? No; each person is only in one of the two sides. > > If not in the second case, union all would probably save the database > some extra work since it won't have to try to weed out duplicates. I'll try that. > > If not in the first case, then wouldn't a limit 200 on the after union > result set work rather than a separate count and subtraction? > Interesting - this would count on the UNION including all cases in the first query before those in the second query. Are UNIONed records presented in any predictable order? ---------------------------------------------------------------------- Andrew J Perrin - http://www.unc.edu/~aperrin Assistant Professor of Sociology, U of North Carolina, Chapel Hill [EMAIL PROTECTED] * andrew_perrin (at) unc.edu ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
