Question

I need to update a table based on another table, so I have the statement:

update FAULTS
set FAULTS.FAULT_STATE = (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID
)

And it gives me error saying:

ORA-01427: single-row subquery returns more than one row

I tried DISTINCT but the state values are different too so DISTINCT does not work. So I changed it too:

update FAULTS
set FAULTS.FAULT_STATE = (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID and rownum = 1
)

Now it does not give errors.

The problem is, if the sub-query returns a null, it will also update the row and clear the content. Any fix for that?

Answer 1

You can ensure only rows with a match are updated like this:

update FAULTS
set FAULTS.FAULT_STATE = (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID and rownum = 1
)
where exists (
    select INCIDENTS.TICKET_STATE from INCIDENTS
    where INCIDENTS.CF_ID = FAULTS.CF_ID
)