Thread: A JOIN question

I am working on a system whee one group of folks inputs portions of data
into a table, and a 2nd completes the data for each row.


The engineers enter in the items they need into a BOM table, and purchasing
agents get quotes and create PO's. There is not a fixed relationship between
the parts (part number and manufacturers) and the vendor (mfg agent or
distributor),  A project manager determines which vendor to buy various
manufacturers items from. This sis controlled by the following table:



CREATE TABLE mfg_vendor_relationship (
    mfg_vendor_relationship_key_serial         integer DEFAULT nextval('ica.mfg_vendor_relationship_key_serial')
    PRIMARY KEY ,
    mfg_key       integer NOT NULL,
    vendor_key    integer NOT NULL,
    project_key   integer NOT NULL,
    modtime       timestamptz NOT NULL DEFAULT current_timestamp ,
    FOREIGN KEY (mfg_key) references mfg(mfg_key) ON DELETE RESTRICT ,
    FOREIGN KEY (vendor_key) references vendor(vendor_key) ON DELETE RESTRICT ,
    FOREIGN KEY (project_key) references project(project_key) ON DELETE RESTRICT ,
    CONSTRAINT mfg_vendor_constraint 
                UNIQUE (
            mfg_key , 
            vendor_key , 
            project_key
        )
);
So, I have the following view for the purchasing agents.


CREATE view t1 as 
select 
    project.proj_no ,
    qty ,
    costing_unit.unit,
    mfg_part.mfg_part_no ,
    mfg.name as m_name ,
    mfg_part.descrip as description ,
    vendor.name as v_name ,
    format_phone_no(
            vendor.area_code,
            vendor.phone_exchange,
            vendor.phone_number,
            vendor.phone_extension) office_phone ,
    cast(cost_per_unit as money) ,
    cast(qty * cost_per_unit as   money) line_ttl ,
    need_date ,
    order_date ,
    received_date ,
    po_no ,
    po_line_item , 
        po_revision ,
        po_rev_date ,
    po_terms_and_conditions.net_interval ,
    po_terms_and_conditions.discount_interval ,
    po_terms_and_conditions.discount
from 
    bom_item 
right join project on 
    project.project_key = bom_item.project_key
inner join mfg_part on 
    mfg_part.mfg_part_key = bom_item.mfg_part_key
inner join costing_unit on 
    costing_unit.costing_unit_key = bom_item.costing_unit_key
inner join mfg on 
    mfg.mfg_key = mfg_part.mfg_key 
inner join mfg_vendor_relationship on
    mfg_vendor_relationship.mfg_key = mfg_part.mfg_key
    AND
    mfg_vendor_relationship.project_key = bom_item.project_key
inner join vendor on
    mfg_vendor_relationship.vendor_key = vendor.vendor_key
FULL OUTER JOIN po_terms_and_conditions ON
    po_terms_and_conditions.po_terms_and_conditions_key = bom_item.po_terms_and_conditions_key
    ;

Now, my problem is that this join:

inner join mfg_vendor_relationship on
    mfg_vendor_relationship.mfg_key = mfg_part.mfg_key
    AND
    mfg_vendor_relationship.project_key = bom_item.project_key

Means that the item to be purchased is invisible to the purchasing agent if
the project manager has not populated the cross reference table.

How can I modify this select so that all items for a given project will
appear in the purchasing agents view?

-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                        -- Benjamin Franklin

On Mon, Dec 30, 2019 at 02:47:53PM -0700, Michael Lewis wrote:
> >
> > LEFT join mfg_vendor_relationship on
> >         mfg_vendor_relationship.mfg_key = mfg_part.mfg_key
> >         AND
> >         mfg_vendor_relationship.project_key = bom_item.project_key
> > LEFT join vendor on
> >         mfg_vendor_relationship.vendor_key = vendor.vendor_key
> >
> 
> Perhaps I am missing something, but it seems like just a matter of changing
> inner join to left so you keep what you already have and augment vendor
> information when it exists. I never use right joins (I re-write to always
> declare as left) so I am not sure if the right join near the top screws
> that up. I might consider using a UNION ALL to combine sets where values
> are NULL with left joins, and use plain (inner) joins for the not nulls.

Thanks. That looks like it gives me what I need.

RE right joins, I just got started doing that, and it is easier for me to
think that way.

-- 
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
                        -- Benjamin Franklin