How to compare two table value using if condition in function of Postgres - postgresql

Question

create or replace function trace.get_latest_exception_custom_msg(id varchar)
returns varchar
language plpgsql
as $$
declare
msg varchar ;
begin
perform t1.message, t1.created_time from table_1 t1 where t1.id = id order by t1.created_time desc limit 1;
perform t2.message, t2.created_time from table_2 t2 where t2.id = id order by t2.created_time desc limit 1;
if date(t1.created_time ) >= date(t2.created_time) then msg= t1.message;
elsif d date(t1.created_time ) < date(t2.created_time) then msg= t1.message;
else msg =t1.message;
end if;
return msg;
end;
while i call this function it give error ERROR: missing FROM-clause entry for table "t_1

Answer 1

You need to store the result of the two SELECT queries into variables in order to be able to be able to use them in an IF statement.
Your IF statement is also a bit confusing as all three parts assign the same value to msg. I assume that you want to use t2.message at least in one case.
create or replace function trace.get_latest_exception_custom_msg(p_id varchar)
returns varchar
language plpgsql
as
$$
declare
t1_msg varchar;
t1_created date;
t2_msg varchar;
t2_created date;
msg varchar;
begin
select t1.message, t1.created_time::date
into t1_msg, t1_created
from table_1 t1
where t1.id = p_id
order by t1.created_time desc
limit 1;
select t2.message, t2.created_time::date
into t2_msg, t2_created
from table_2 t2
where t2.id = p_id
order by t2.created_time desc
limit 1;
if t1_created >= t2_created then
msg := t1_msg;
elsif t1_created < t2_created then
msg := t2_msg; --<< ???
else
-- this can only happen if one (or both) of the DATEs is NULL.
msg := t1_msg;
end if;
return msg;
end;
$$