2 ms·

PL/SQL is not SQL.

• kqr 7y ago
  Do recursive CTEs count as SQL, then? Despite the name, they are practically loops.
  • kragen 7y ago
    I wrote this query for Dercuano the other day; it computes the Collatz sequence starting from each of the first 100 integers, running a second Collatz computation twice as fast in parallel to detect any cycles (and of course there are none): with recursive collatz as (select 1 as x, 1 as n, 1 as m, 0 as p, 0=1 as exit union select case when nextx then x + 1 else x end as x, case when nextx then x + 1 else (case n % 2 when 1 then 3*n + 1 else n / 2 end) end as n, case when nextx then x + 1 else (case newm % 2 when 1 then 3*newm + 1 else newm / 2 end) end as m, case when nextx then 0 else p+1 end as p, case when nextx then 0 = 1 else n = newm end as exit from (select (m = 1 or newm = 1) as nextx, x, n, m, p, newm from (select x, n, m, p, case m % 2 when 1 then 3*m + 1 else m / 2 end as newm from collatz where not exit) a) b where x < 100) select * from collatz; It works in Postgres 9.5.14; I'm interested to hear if it works or doesn't in other SQL implementations. I think this definitely qualifies as a loop.