# select*fromunnest(array[array['a', 'b'], array['c', 'c']]),unnest(array[array['1', '2'], array['3', '4']]);ERROR: 42712: table name "unnest" specified more than once
This specific error is resolved by using the alias feature of the FROM clause:
aliasA substitute name for the FROM item containing the alias. An alias is used for brevity or to eliminate ambiguity for self-joins (where the same table is scanned multiple times)
I’m trying to cross-join multiple two-dimensional arrays, expecting to retain the inner arrays. I’ve been trying for hours without luck; the ever-esoteric SQL syntax foils me at every turn.It’s a shame I can’t get the unnest function not to just concatenate the inner arrays if I just put a bunch of them. This doesn’t strike me as optimal behavior.
Putting unnest in a select-list might get you closer to your goal. Or the array-array concatenating operator.
For more context, I’m trying to make a system of functions to score a Texas Hold ‘Em game. So I have a card type consisting of a pair of suit and rank, and I’m tossing them about. The cross-join is so I can build all candidate hands for scoring. I’m trying to create a function I can call like this:selectbest_hands_with_river(array[c('H', 'K'),c('D', 'A')],array[c('C', '2'),c('C', 'K'),c('S', 'K'),c('H', 'A'),c('C', 'A')])Here, c is a function that constructs a card type. Card is a ROW(varchar, varchar).So: how do I cross-join three identical arrays of my card type?
Something like:
Select f1.a, f2.b
From (select * from unnest(arr)) as f1 (a)
Cross join (select * From unnest(arr)) as f2 (b)
Etc...Maybe with parentheses...
There may be a more succinct way to write this but going verbose until it works minimizes the amount of syntax you need to deal with. Though I personally encourage writing intentional cross join (really, all joins) using join syntax instead of comma-separated from items.
David J.
