Question

I use following query to insert a new row:

insert into table1 (c1, c2, c3) (select c1, c2, c3 from table2 where some_condition)

This works finely if there is a row in table2 that satisfies some_condition. But if there are no rows, nothing is inserted.

Are there any way to specify default values to insert if select returns empty result set? I want to do that in one sql query.

Answer 1

This isn’t very pretty, but it does what you want, You’d need to test with your environment to see if it performs well enough

SQL> drop table so_tgt;

Table dropped.

SQL> 
SQL> create table so_src (
  2   c1 varchar2(6)
  3  ,c2 varchar2(6)
  4  ,c3 varchar2(6)
  5  );

Table created.

SQL> 
SQL> insert into so_src values ( 'foo','bar','moo' );

1 row created.

SQL> 
SQL> create table so_tgt as select * from so_src where 1 = 0;

Table created.

SQL> 
SQL> /* Test for existing row insert */
SQL> insert into so_tgt
  2  with x as ( select s.*, 1 as r
  3          from so_src s
  4          where c1='foo'
  5          union
  6          select 'x','y','z',0 as r /* DEFAULT VALUES */
  7          from dual )
  8  select c1,c2,c3
  9  from x
 10  where r = ( select max(r) from x ) ;

1 row created.

SQL> 
SQL> select * from so_tgt;

C1     C2     C3
------ ------ ------
foo    bar    moo

SQL> truncate table so_tgt;

Table truncated.

SQL> 
SQL> /* Test for default row insert */
SQL> insert into so_tgt
  2  with x as ( select s.*, 1 as r
  3          from so_src s
  4          where c1='far'
  5          union
  6          select 'x','y','z',0 as r /* DEFAULT VALUES */
  7          from dual )
  8  select c1,c2,c3
  9  from x
 10  where r = ( select max(r) from x ) ;

1 row created.

SQL> 
SQL> select * from so_tgt;

C1     C2     C3
------ ------ ------
x      y      z

SQL> truncate table so_tgt ;

Table truncated.