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: 
restrict the output of the inner query to one value to successfully run your query.

```
select l.student_code
from school_table l, student_table n
where l.school = n.schoolname 

```

[check this](http://www.techonthenet.com/oracle/errors/ora01427.php)
Try to add and rownum=1 to your subquery conditions if you DO NOT care about the value from the list or DO sure that they are the same.