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