Oracle SQL - Subquery Joining Condition

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Introduction

Oracle does not discriminate between meaningful and meaningless questions. You have only two constraints:

  • The data types must match, or assignable with implicit data type conversion.
  • The subquery should not select too many column values per row.

Subquery Returns Too Many Values

Error: Subquery Returns Too Many Values 

select attendee 
from   registrations 
where  course in 
      (select course, begindate 
       from   offerings 
       where  location = 'CHICAGO'); 
      (select course, begindate 
       * 
ERROR at line 4: 
ORA-00913: too many values

Here, the subquery returns (COURSE, BEGINDATE) value pairs, which cannot be compared with COURSE values.

However, you can compare attribute combinations with subqueries in SQL. To fix the error:

Demo

SQL>
SQL> drop table offerings;

Table dropped.-- from   w  w  w  .  j  a va  2 s . c o  m

SQL> create table offerings(
  2  course     VARCHAR2(6)  not null,
  3  begindate  DATE         not null,
  4  trainer    NUMBER(4)            ,
  5  location   VARCHAR2(8)) ;
SQL>
SQL> insert into offerings values ('SQL',date '1999-04-12',7902,'DALLAS' );
SQL> insert into offerings values ('JSON',date '1999-08-10',7004,'CHICAGO');
SQL> insert into offerings values ('SQL',date '1999-10-04',7001,'SEATTLE');
SQL> insert into offerings values ('SQL',date '1999-12-13',7001,'DALLAS' );
SQL> insert into offerings values ('JAVA',date '1999-12-13',7004,'SEATTLE');
SQL> insert into offerings values ('XML',date '2000-02-03',7001,'DALLAS' );
SQL> insert into offerings values ('JAVA',date '2000-02-01',7011,'DALLAS' );
SQL> insert into offerings values ('PLS',date '2000-09-11',7008,'DALLAS' );
SQL> insert into offerings values ('XML',date '2000-09-18',NULL,'SEATTLE');
SQL> insert into offerings values ('JSON',date '2000-09-27',7902,'DALLAS' );
SQL> insert into offerings values ('ERM',date '2001-01-15',NULL, NULL    );
SQL> insert into offerings values ('PRO',date '2001-02-19',NULL,'DALLAS' );
SQL> insert into offerings values ('RSD',date '2001-02-24',7008,'CHICAGO');
SQL>
SQL> drop table registrations;

Table dropped.

SQL> create table registrations(
  2  attendee    NUMBER(4)   not null,
  3  course    VARCHAR2(6) ,
  4  begindate   DATE      not null,
  5  evaluation  NUMBER(1)   check (evaluation in (1,2,3,4,5))) ;
SQL>
SQL> insert into registrations values (7002,'SQL',date '1999-04-12',4   );
SQL> insert into registrations values (7934,'SQL',date '1999-04-12',5   );
SQL> insert into registrations values (7006,'SQL',date '1999-04-12',4   );
SQL> insert into registrations values (7011,'SQL',date '1999-04-12',2   );
SQL> insert into registrations values (7008,'SQL',date '1999-10-04',NULL);
SQL> insert into registrations values (7009,'SQL',date '1999-10-04',3   );
SQL> insert into registrations values (7902,'SQL',date '1999-10-04',4   );
SQL> insert into registrations values (7902,'SQL',date '1999-12-13',NULL);
SQL> insert into registrations values (7006,'SQL',date '1999-12-13',NULL);
SQL> insert into registrations values (7003,'JSON',date '1999-08-10',4   );
SQL> insert into registrations values (7012,'JSON',date '1999-08-10',4   );
SQL> insert into registrations values (7902,'JSON',date '1999-08-10',5   );
SQL> insert into registrations values (7010,'JSON',date '2000-09-27',5   );
SQL> insert into registrations values (7002,'JAVA',date '1999-12-13',2   );
SQL> insert into registrations values (7007,'JAVA',date '1999-12-13',NULL   );
SQL> insert into registrations values (7011,'JAVA',date '1999-12-13',5   );
SQL> insert into registrations values (7008,'JAVA',date '1999-12-13',5   );
SQL> insert into registrations values (7009,'JAVA',date '1999-12-13',4   );
SQL> insert into registrations values (7004,'JAVA',date '2000-02-01',3   );
SQL> insert into registrations values (7008,'JAVA',date '2000-02-01',4   );
SQL> insert into registrations values (7006,'JAVA',date '2000-02-01',5   );
SQL> insert into registrations values (7012,'XML',date '2000-02-03',4   );
SQL> insert into registrations values (7002,'XML',date '2000-02-03',5   );
SQL> insert into registrations values (7004,'PLS',date '2000-09-11',NULL);
SQL> insert into registrations values (7002,'PLS',date '2000-09-11',NULL);
SQL> insert into registrations values (7011,'PLS',date '2000-09-11',NULL);
SQL> select attendee
  2  from   registrations
  3  where (course, begindate) in
  4        (select course, begindate
  5         from   offerings
  6         where  location = 'CHICAGO');

 ATTENDEE
---------
 07003.00
 07012.00
 07902.00

SQL>

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