Problems in oracle SQL using select in update - sql

Question

So, i have 2 tables, for simplicity's sake i'll show 2 columns for one, and only one for the other, but they have a lot more data.
ok, so, the tables looks like this:
_________________________________
| table 1 |
+---------------------------------+
| gas_deu est_pag |
+---------------------------------+
| 56857 (null) |
| 60857 (null) |
| 80857 (null) |
+---------------------------------+
______________________
| table 2 |
+----------------------+
| gas_pag |
+----------------------+
| 56857 |
| 21000 |
| 75857 |
+----------------------+
table 1 and table 2 can be joined using id_edi, and nr_dep (same name in both tables)
what's happening here is basically the following:
in table 1, i have gas_deu which is a number owned to someone.
in table 2 gas_pag is how much has been paid, meaning gas_deu-gas_pag should give 0 (or negative) if gas_deu was paid in full, or a positive number if it was partially paid
Also, some rows from table 1 are not in table 2 meaning gas_deu has not been paid at all.
What i need to do is update est_pag in table 1 with the following:
if gas_deu-gas_pag<=0 (debt paid) then update est_pag value to 1
if gas_deu-gas_pag>0 (partially paid) then update est_pag value to 2
if a row is in table 1 but not in table 2, it has not been paid at all so est_pag value will be 3
I have tried a lot, and i mean A LOT of code in the update for this, the tables have a lot of columns so i won-t post the code i have tried because it would only get more confusing
I mostly tried using select sub-queries in the set of the update, and in the where of the update. all of them always give me the single row error, i know this happens because it returns more than one value, but the how would i do this? I don't see a way in which i get only one value of the query and update only the rows that match the debt status.
using case was the logical choice for me but it always returns more than one row it seems (tried to make a (case when gas_deu-gas_pag<=0 then 1 else est_pag end), since if i could get at least one value in there, it would be a start, but get the same more than one row problem)
Any help or suggestions are highly appreciated,i already tried everything i could think of, and a lot of answers from here in stackoverflow, but still can't get it to work out
Edit: adding what table 1 should look like after updating
| table 1 |
+---------------------------------+
| gas_deu est_pag |
+---------------------------------+
| 56857 1 |
| 60857 2 |
| 80857 2 |
+---------------------------------+
Update 2:
update table1
set est_pag=(select (case when (select min((case when gasto.gas_deu-
pago.gas_pag<=0 then 0 else null end))
from table2 pago full outer join gasto_comun_pruebaestpago gasto on
pago.nr_dep=gasto.nr_dep
where gasto.nr_dep=pago.nr_dep and gasto.id_edi=pago.id_edi)=0 then 1 else
null end)
from table2 pago full outer join gasto_comun_pruebaestpago gasto on
pago.nr_dep=gasto.nr_dep
where gasto.nr_dep=pago.nr_dep and gasto.id_edi=pago.id_edi)
where est_pag is null;
This is one of many codes i tried. this one changes all values to 1, this is bacause of the min() in there, that outpust just one row, with a 0 and the gets checked by the case, 0=0 so everything goes to 1. The problem is that, without the min(), the select does what i need, but the update throws the 'single-row subquery returns more than one row' error again

Answer 1

You can update through a left outer join. It is possible the second table has more than one payment for the same account (customers may make partial payments), so I aggregate the second table by ID first. You didn't provide input data for testing, so in my small test I assume the tables are matched by id (primary key in the first table, foreign key in the second table - even though I didn't write the constraints into the table definitions).
The way I wrote the update, a 3 will be assigned if an account is not present in the second table, but also if it is present but with NULL in the gas_pag column. (It would be best if that column was declared NOT NULL from the outset!) If a different handling is desired in that case, you didn't say; it can be accommodated easily though.
So, here goes.
TABLE CREATION
create table t1 ( id number, gas_deu number, est_pag number );
insert into t1
select 101, 56857, null from dual union all
select 104, 60857, null from dual union all
select 108, 80857, null from dual
;
create table t2 ( id number, gas_pag number ) ;
insert into t2
select 101, 56857 from dual union all
select 104, 60000 from dual
;
select * from t1;
ID GAS_DEU EST_PAG
---------- ---------- ----------
101 56857
104 60857
108 80857
select * from t2;
ID GAS_PAG
---------- ----------
101 56857
104 60000
UPDATE STATEMENT
update
( select est_pag, gas_deu, gas_pag
from t1 left join
( select id, sum(gas_pag) as gas_pag from t2 group by id ) x
on t1.id = x.id
)
set est_pag = case when gas_deu <= gas_pag then 1
when gas_deu > gas_pag then 2
else 3
end
;
select * from t1;
ID GAS_DEU EST_PAG
---------- ---------- ----------
101 56857 1
104 60857 2
108 80857 3
CLEAN-UP
drop table t1 purge;
drop table t2 purge;