hi I want to union 2 tables but I am not sure if the table is exits
this is my query:
select a from table
union
select case when exists(select a from table1) then (select a from table1)
else (select a from table2) end;
got this
ERROR: ERROR 4840: Subquery used as an expression returned more than one row
I need to use limit 1 in a subquery but it's not the result that I wanted.
do you have other suggestions?
thanks
table, for example, I just created them in my local env for testing:
table 1
CREATE TABLE public.table1
(
a int,
b varchar(80),
c int
);
CREATE TABLE public.table
a int,
b varchar(80),
c int
);
Best Answer
In principle this won't work, as you can't check if table exists and then join it in a query.
The error is unrelated. You are selecting a value in a subselect and it returns multiple rows, as the table exists.
What you can do is: