Q:

Nested SELECT in Oracle

I'm trying to do as follows,
    SELECT ID_ESTACIONAMIENTO
    FROM ESTACIONAMIENTO
    WHERE '-33.52053824804071,-70.68874349999999' 
= (SELECT LATITUD_ESTACIONAMIENTO||','||LONGITUD_ESTACIONAMIENTO FROM ESTACIONAMIENTO);

But returns
ORA-01427: single-row subquery returns more than one row
01427. 00000 -  "single-row subquery returns more than one row"
*Cause:    
*Action:

How can I get ID_ESTACIONAMIENTO WHERE values (in this case '-33.52053824804071,-70.68874349999999') are being compared with a concat query ?

A:

I think a better approach is to just check the latitude and longitude columns separately:
SELECT ID_ESTACIONAMIENTO
FROM ESTACIONAMIENTO
WHERE LATITUD_ESTACIONAMIENTO = '-33.52053824804071' AND
      LONGITUD_ESTACIONAMIENTO = '-70.68874349999999'

Note that you may not need to use quotes if your latitude/longitude data be stored in a numeric column.
If you want to "fix" your exact current query, then just use the concatenated columns from the outer query directly in your WHERE clause:
SELECT ID_ESTACIONAMIENTO
FROM ESTACIONAMIENTO
WHERE LATITUD_ESTACIONAMIENTO||','||LONGITUD_ESTACIONAMIENTO =
      '-33.52053824804071,-70.68874349999999'

By the way, the reason behind your error, which is self-explanatory, is that the subquery returns more than one row.  Actually, it should return every row from the ESTACIONAMIENTO table.

