On Wed, Feb 27, 2008 at 7:39 AM, Kynn Jones <
kynnjo@gmail.com> 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
