ORA-01427: single-row subquery returns more than one row tips Oracle Error Tips by Donald Burleson(S. Karam)

 

The Oracle docs note this on the ORA-01427 error*:

On Oracle Server and PL/SQL User Forum, Adam Wilbur received an ORA-01427 error code and received this information:

Question

Posted by 'Adam Wilbur' on April 21, 2001 at 20:37:00 EST:

Here's what I am trying to do...

UPDATE TABLEA SET TABLEA.COLUMN1 =
(select TABLEB.COLUMN1 FROM TABLEA, TABLEB
WHERE TABLEB.COLUMN2 = 'String Value'
AND TABLEA.COLUMN3 = TABLEB.COLUMN3
AND TABLEA.COLUIMN4 = TABLEB.COLUMN4
AND TABLEB.VALUENAME = 'String Value');

This query returns multiple rows, all of which I need to update in TABLEA.

How do I do this without getting ORA-01427 error?

Answer

Dmytro offered this advice to resolve ORA-01427:

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.

Single Row Subquery

A single row subquery returns only one row. It can be used with the equal comparison operators (=,<,>,<>, etc).

SQL> select
2 order_number
3 from
4 sales
5 where quantity = (select
6 max(quantity)
7 from
8 sales);

ORDER_NUMBER
--------------------
O161

Here, we get the order number for the order that contains the max quantity value. The outer query can return multiply rows, but the subquery can only return one row.

SQL> select
2 order_number
3 from
4 sales
5 where quantity > (select
6 avg(quantity)
7 from
8 sales);

ORDER_NUMBER
--------------------
O118
O149
O157
O161
O167
O179
O183
O186
O189
O193
O196
O197
O198
O199

14 rows selected.

Here, we want the order numbers where the order quantity is above the average quantity in the sales table. Notice that the subquery returns one and only one row that used in the filter.

 

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Helpful Links:

You may want to refer to these helpful links concerning single and multi row subqueries, and tips on deleting rows while avoiding ORA-01427 by Don Burleson.