Question

Here’s a simplified version of my table.

CREATE TABLE TBLAGENT(AGENTID NUMBER, NUMBERSENT NUMBER, AGENTNAME VARCHAR2(100));
INSERT INTO TBLAGENT VALUES(100,NULL,'KNIGHT');
INSERT INTO TBLAGENT VALUES(200,NULL,'SUPES');
INSERT INTO TBLAGENT VALUES(300,NULL,'SPIDEY');

CREATE TABLE TBLSERVICES(AGENTID NUMBER, SERVICES NUMBER);
INSERT INTO TBLSERVICES VALUES(100,44);
INSERT INTO TBLSERVICES VALUES(200,13);
INSERT INTO TBLSERVICES VALUES(300,24);
INSERT INTO TBLSERVICES VALUES(100,34);
INSERT INTO TBLSERVICES VALUES(200,13);
INSERT INTO TBLSERVICES VALUES(300,24);

SELECT TA.AGENTID, SUM(SERVICES), TA.AGENTNAME, TA.NUMBERSENT 
       FROM TBLAGENT TA, TBLSERVICES TS
       WHERE TA.AGENTID = TS.AGENTID
       GROUP BY TA.AGENTID, TA.AGENTNAME, TA.NUMBERSENT

The requirement is to update the NUMBERSENT column in the tblAgent table with the SUM(Services) from tblServices table.

I came up with this update statement.

/*Works*/
UPDATE tblagent t
   SET t.numbersent =
       (SELECT SUM(services)
          FROM tblservices x
         WHERE t.agentid = x.agentid
         GROUP BY x.agentid)

When I change the syntax of this statement to INNER JOIN syntax, it fails.

/*Throws an error*/
UPDATE tblagent t
   SET t.numbersent =
       (SELECT SUM(services)
          FROM tblservices x INNER JOIN tblAgent t
         ON t.agentid = x.agentid
         GROUP BY x.agentid)

This throws up an error ORA-01427: single-row subquery returns more than one row

Why would the second statement throw an error?

Answer 1

@Tony Andrews is right and if you still want to use INNER JOIN you should write this:

 UPDATE tblagent t1
   SET t1.numbersent =
       (SELECT SUM(services)
          FROM tblservices x INNER JOIN tblAgent t
         ON t.agentid = x.agentid
         GROUP BY x.agentid
         having t1.agentid = x.agentid)

(To have upper and inner DML one common column,for not to return more than one row)

But of course I think this is just complicating your job and nothing more..Use the first variant…This is better Advice.