Question: I am trying to update a column based on another column in the same table (student table) and a column
from another table (school table)

Code is:

```
update student_table
set student_code =
(select l.student_code
from school_table l, student_table n
where l.school = n.schoolname)

```

I get the following error

ORA - 01427 Single-row subquery returns more than one row

Any help would be appreciated.

Answer: 
If you run your subquery you'll find it returning more than one row. You are trying to update a column to be equal to the result of your subquery so it expects only one value. You should limit your subquery to only return one row such as using max() or min() or, perhaps you meant to join to the outer student\_table? Try:

```
update student_table n
set student_code =
(select l.student_code
from school_table l
where l.school = n.schoolname);

```
We all know exactly what the error says. SET only expects one value per column to be set. What we want to achieve is Update all rows for a given column using values from another table's column.

Now here's the solution:

```
BEGIN
For i in (select col_X, col_Y from table1) 
LOOP
Update table2 set col1 = i.col_X where col2 = i.col_Y;
END LOOP;
END;

```

That's how exactly you run it on SQLDeveloper worksheet. They say it's slow but that's the only solution that worked for me on this case.