On Wed, Feb 27, 2008 at 7:39 AM, Kynn Jones <[EMAIL PROTECTED]> wrote:
> Suppose I have two tables, A and B, with k(A) and k(B) columns > respectively, and let's assume to begin with that they have the same number > of rows r(A) = r(B) = r. > What's the simplest way to produce a table C having r rows and k(A) + k(B) > columns, and whose i-th row consists of the k(A) columns of the i-th row of > A followed by the k(B) columns of the i-th row of B (for i = 1,...,r)? (By > "i-th row of A" I mean the i-th row of the listing one would get from > "SELECT * FROM A", and likewise for B.) > Expanding on my own post here, it occurred to me that it would be very nice to have a function (say) index, that, when used in a SELECT list, would yield the position in the corresponding table of the current row. E.g. the expression SELECT index(*) FROM A; would produce the same table as SELECT generate_series( 1, r(A) ); It would also be useful to have a "subscripting function" s (which may be regarded as somewhat of the inverse of index()) that, given a table expression E, and an "index expression" I (which could be a single index or range, or a list of such), will return the table consisting of the rows in E designated by the indices in I). For example, either one these queries SELECT s( A, 1, 2, 3 ); SELECT * FROM s( A, 1, 2, 3 ); would produce the same table as SELECT * FROM A LIMIT 3; Does anything like index() or s() exist? If not, are there other functions that may be useful in an implementation of index() or s()? Thanks! Kynn
