FW: Undelivered Mail Returned to Sender

I apologize for asking, what I suspect will turn out to be a newbie
question, but I have managed to get myself quite confused on this.

I am defining a view as follows


CREATE OR REPLACE view purchase_view as 
select 
    project.proj_no ,
    qty ,
    mfg_part.mfg_part_no ,
    mfg.name as m_name ,
    mfg_part.descrip as description ,
    ( 
    SELECT 
        name
    FROM
        vendor
    WHERE
        bom_item.vendor_key =
        (
            SELECT
                vendor_key
            FROM
                mfg_vendor_relationship
            WHERE
                bom_item.mfg_key = mfg_key
            AND
                prefered = TRUE
            AND
                bom_item.project_key = project_key
                
        )
    ) 
    as v_name ,
    /*
    vendor.name as v_name ,
    */
    cost_per_unit ,
    costing_unit.unit,
    need_date ,
    order_date ,
    recieved_date ,
    po_no ,
    po_line_item 
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 vendor on 
    vendor.vendor_key = bom_item.vendor_key
inner join costing_unit on 
    costing_unit.costing_unit_key = bom_item.costing_unit_key
inner join mfg on 
    mfg.mfg_key = bom_item.mfg_key 
WHERE bom_item is NOT NULL  
ORDER BY 
    project.proj_no ,
    mfg_part
    ;

Most of the tables are pretty much simple key -> value relationships for
normalization. I can add the create statements to this thread if it adds
clarity.

The exception is:



CREATE TABLE mfg_vendor_relationship (
    mfg_vendor_relationship_key_serial         integer DEFAULT nextval('mfg_vendor_relationship_key_serial')
    PRIMARY KEY ,
    mfg_key       integer NOT NULL,
    vendor_key    integer NOT NULL,
    project_key   integer NOT NULL,
    prefered      boolean NOT NULL ,
    modtime           timestamptz DEFAULT current_timestamp ,
    FOREIGN KEY (mfg_key) references mfg(mfg_key) ,
    FOREIGN KEY (vendor_key) references vendor(vendor_key) ,
    FOREIGN KEY (project_key) references project(project_key) ,
    CONSTRAINT mfg_vendor_constraint 
                UNIQUE (
            mfg_key , 
            vendor_key , 
            project_key
        )
);


I am down to having a single row in the mfg_vendor_relationship as follows:

 mfg_vendor_relationship_key_serial | mfg_key | vendor_key | project_key |
 prefered |            modtime            
 ------------------------------------+---------+------------+-------------+----------+-------------------------------
                 164 |       1 |          1 |           2 |
                 t        | 2019-08-10 14:21:04.896619-04

But trying to do a select * from this view returns:

ERROR:  more than one row returned by a subquery used as an expression

Can someone please enlighten me as to the error of my ways?


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


----- End forwarded message -----

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