PostgreSql: how to update table from array? - postgresql

Question

How to update table fields from array to avoid temp table using?
User passes array to reorder table.
create TABLE items
(
id serial primary key,
name text,
select_order int
)
insert into items(name, select_order)
values
('cucumber',0),
('milk',1),
('coffee',2),
('water',3)
select * from items order by select_order;
DO
$body$
DECLARE var_array int[]:='{3,0,2,1}';
BEGIN
update items ??
END;
$body$
The final result in this example should be
select * from items order by select_order;
name select_order
------------------------
water 0
cucumber 1
coffee 2
milk 3

Answer 1

Assuming the index in the array corresponds to the value in select_order the following query returns the new and old value:
select i.id, i.select_order, t.new_sort
from items i
join lateral unnest(array[3,0,2,1]) with ordinality as t(new_sort, idx) on t.idx - 1 = i.select_order
Now this can be used to update the target table:
update items
set select_order = r.new_sort
from (
select i.id, i.select_order, t.new_sort
from items i
join lateral unnest(array[3,0,2,1]) with ordinality as t(new_sort, idx) on t.idx - 1 = i.select_order
) r
where r.id = items.id;
This also assumes that select_order starts a 0 and has no gaps.