Question

this is not a real example, it is something that has been bugging me for some time, and I’d be very thankful to anyone who can explain this behavior.

I have these two tables

MYTABLE1
ID  TYPE    NAME 
1   1       typea
2   2       typea
3   3       typea
4   4       typeb
5   5       typeb
6   6       typeb
7   7       typec
8   8       typec
9   9       typec
10  10      typed

MYTYPE
ID  NAME    DESCRIPTION
1   typea   typea with desc
2   typea   
3   typea   TYPE
4   typeb   typeb with desc
5   typeb   
6   typeb   TYPE
7   typec   typec with desc
8   typec   
9   typec   TYPE

I’d like to have a sql that returns rows from both tables (mytable1 a, mytype b) where

a) MYTABLE1.type = MYTYPE.ID and MYTYPE.description=’TYPE’

b) MYTABLE1.type is not in MYTYPE.id

a.id    a.type  a.name  b.id    b.name  b.description
3       3       typea   3       typea   TYPE
6       6       typeb   6       typeb   TYPE
9       9       typec   9       typec   TYPE
10      10      typed   null    null    null

I have tried this statements with no success. I want a solution that uses outer joins, not unions or nested selects.

For the example, I am using Oracle outer join syntax but I think the same result can be achieved by using standard syntax and putting the condition a) inside the ON clause or b)in the where clause

What I’d like is to understand the “strange” behaviour of them, and try to find one that works for the example provided.
Most strange for me it is SQL2. I am not writing the results of the queries, to keep the question shorter, but I can provide them if needed.

SQL1

select * 
from 
  mytable1 a,
  mytype b
where
  a.type=b.id(+)
  and b.description ='TYPE'
order by a.id

SQL2

select * 
from 
  mytable1 a,
  mytype b
where
  a.type=b.id(+)
  and b.description(+) ='TYPE'
order by a.id

SQL3

select * 
from 
  mytable1 a,
  mytype b
where
  a.type=b.id(+)
  and (b.description ='TYPE' or b.description is null)
order by a.id

Thanks in advance,

Answer 1

Stop using old Cartesian product syntax. JOIN syntax is the ANSI-92 standard. 20 years should be enough to be considered stable…

SELECT
  *
FROM
  myTable1    a
LEFT JOIN
  myType      b
    ON b.id = a.type
WHERE
     b.description = 'TYPE'
  OR b.id IS NULL

NOTE: I did have b.description IS NULL but, as far as I recall, ORACLE treats 0 length strings as NULL. Therefore it is better to test the id field for a case of No Join.