Update all rows for one column in a table with data in another table - sql

Question

I appreciate any advice on this..
I have two tables where I have to update a column in my primary table with data that resides in another secondary table. I cannot rely on views, etc as this data has to be able to be edited by the user in APEX in the future. I am basically pre-populating the data for the users to reduce their manual entry.
Primary Table = Table 1
Secondary Table = Table 2
Columns to be updated in Table 1 = FTE_ID, ACCOUNT_TYPE
Columns where the data will come from Table 2 = R_ID, ACCOUNT_TYPE
Common column in both tables = TABLE1.FID AND TABLE2.FID
Here is what I have tried, but I get "single-row subquery returns more than one row" because there are multiple table1.fid rows in table1. I basically want to perform this update for ALL rows where TABLE1.FID = TABLE2.FID.
Here is my attempt:
UPDATE TABLE1
SET TABLE1.FTE_ID =
(SELECT TABLE2.R_ID FROM TABLE2 WHERE TABLE1.FID = TABLE2.FID);
Error:
single-row subquery returns more than one row
Thanks for your help,

Answer 1

You can fix the proximate problem by using aggregation or row number:
UPDATE TABLE1
SET TABLE1.FTE_ID = (SELECT MAX(TABLE2.R_ID)
FROM TABLE2
WHERE TABLE1.FID = TABLE2.FID
);
The subquery can only return one row; it is an "arbitrary" value from the possible matching values.
If the field is a character field and you want all matching values, then perhaps listagg is more appropriate:
UPDATE TABLE1
SET TABLE1.FTE_ID = (SELECT LISTAGG(t2.R_ID, ',') WITHIN GROUP (ORDER BY t2.R_ID)
FROM TABLE2 t2
WHERE TABLE1.FID = t2.FID
);