Unique constraint fired when updating in MERGE statement.

Question

Hi guys
I have an issue which I am unable to resolve. Would appreciate any help on this. The data setup and the scenario is as below.
SQL*Plus: Release 10.2.0.1.0 - Production on Wed May 4 11:46:02 2011
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
SQL>
create table table_1
(id number,
id_name varchar2(20));
Alter table table_1 add primary key(id);
create table table_2
(id number,
id_name varchar2(20));
insert into table_2 values (1, 'id_1');
insert into table_2 values (2, 'id_2');
insert into table_2 values (1, 'id_1_upd');
SQL> select * from table_1;
no rows selected
SQL> select * from table_2;
        ID ID_NAME
         1 id_1
         2 id_2
         1 id_1_upd
SQL>
SQL>  merge into table_1 target
  2   using (select id,
  3                 id_name
  4            from table_2) source
  5   on (source.id = target.id)
  6   when matched then
  7      update set target.id_name = source.id_name
  8   when not matched then
  9      insert(id,
10             id_name)
11      values(source.id,
12             source.id_name);
merge into table_1 target
ERROR at line 1:
ORA-00001: unique constraint (SYS_C00137508) violated
SQL> ed
Wrote file afiedt.buf
  1  select constraint_type, table_name, status
  2*   from user_constraints where constraint_name = 'SYS_C00137508'
SQL> /
C TABLE_NAME                     STATUS
P TABLE_1                        ENABLEDCan someone please help me in resolving this as the actual code that I am developing has the same setup and I am constantly getting this error. So long as the same record does not come up in the "source" table, MERGE does either an update or an insert.
But as soon a "duplicate" record comes up for updation, I am getting the unique constraint error.
Thanks
- K.B.

Answer 1

Dear,
ERROR at line 1:
ORA-00001: unique constraint (SYS_C00137508) violatedYou need to think about two things
(a) read consistency : what was the situation of table_1 when the maching clause has been initially evaluated ; there were 0 rows matching which means the merge operation will be all insert
(b) your matching clause has a problem : the join column must be unique in both tables otherwise the merge will be ambigous. You don't have a unique key on the source table
(c) think that the merge operation will never insert id =1 and then update id = 1 within the same operation. This will never happen
Hope this helps
Mohamed Houri