Question

Here is problem I have:

Table A
id_a |   name
---------------------
1 |   name-A
2 |   name-B
3 |   name-C
4 |   name-D
5 |   name-E
6 |   spcial_type

Table B
id_b | id_a | condition | subtype
-------------------------------------------------
1    | 2    | 1      | 1
2    | 1    | 0      | 1
3    | 1    | 1      | 2
4    | 2    | 0      | 1
5    | 4    | 0      | 1
6    | 5    | 1      | 1
7    | 2    | 1      | 3

Terms:
Table A: “special_type” exluded
Table A: rows not present in Table B included
Table B: all with condition=0 exluded

Result Table:
id_r | id_a | id_b | name | condition
-----------------------------------------------
1    | 1    | 3    | name-A    | 1
2    | 2    | 1    | name-B    | 1
3    | 5    | 6    | name-E    | 1
4    | 2    | 7    | name-B    | 1
5    | 3    | null | name-C    | null

table A.subtype is only aux. to show that id_a can be stored many times with condition=1

What I tried:

select x.id_a, x.name, z.id_b, z.id_a, z.condition from Table A 
LEFT JOIN Table z ON x. id_a = z. id_a 

but this got me items with condition=0, which I do not want

so I tried:

 
select x.id_a, x.name, z.id_b, z.id_a, z.condition from Table A 
LEFT JOIN Table z ON x. id_a = z. id_a where z.condition=1

but that idea excluded items from Table A not present in Table B, and I want these items.

Can it be don inside of MySQL, or do I need scripting lang. to sort it out?

Thoughts anyone?

Answer 1

OK
I must have had a temp. black out.
Here it is:

select x.id_a, x.name, z.id_b, z.id_a, z.condition from Table A 
LEFT JOIN Table z ON x. id_a = z. id_a AND z.condition=1

condition below

AND z.condition=1

was the key, when placed in join condition not in where clause