Puedes unirte en la location_distance
tabla dos veces usando un LEFT JOIN
y luego use COALESCE()
función para devolver el valor correcto para la distance
:
select ot.id,
ot.fromlocid,
ot.tolocid,
ot.otherdata,
coalesce(ld1.distance, ld2.distance) distance
from other_table ot
left join location_distance ld1
on ld1.fromLocid = ot.toLocid
and ld1.toLocid = ot.fromLocid
left join location_distance ld2
on ld2.toLocid = ot.toLocid
and ld2.fromLocid = ot.fromLocid
Consulte SQL Fiddle con demostración
Esto devuelve el resultado:
| ID | FROMLOCID | TOLOCID | OTHERDATA | DISTANCE |
---------------------------------------------------
| 12 | 5 | 3 | xxxx | 70 |
| 22 | 2 | 4 | xxxx | 63 |
| 56 | 8 | 6 | xxxx | 15 |
| 78 | 3 | 5 | xxxx | 70 |