Restricting values in a table used in a FULL OUTER JOIN - sql

Question

This concerns Oracle SQL.
Considering the following 3 tables:
TRIP_SEGMENT:
CREATE TABLE TRIP_SEGMENT(
SEG_ID NUMBER(6) NOT NULL,
DIRECTION VARCHAR(8) NOT NULL,
DEPARTURE_LOCATION VARCHAR(50) NOT NULL,
DESTINATION VARCHAR(50) NOT NULL,
SEGMENT_PRICE NUMBER(5,2) NULL,
TRIP_ID NUMBER(6) NOT NULL,
CONSTRAINT chk_SEG_DIRECTION CHECK (DIRECTION IN ('Outbound','Inbound')),
CONSTRAINT pk_SEGMENT PRIMARY KEY (SEG_ID),
CONSTRAINT fk_TRIP_ID FOREIGN KEY (TRIP_ID) REFERENCES TRIP(TRIP_ID)
);
TRANSPORTATION:
CREATE TABLE TRANSPORTATION(
TRANSP_BOOK_ID NUMBER(6) NOT NULL,
TRANSP_PRICE NUMBER(5,2) NULL,
DEPARTURE_DATE DATE NULL,
ARRIVAL_DATE DATE NULL,
EXT_BOOK_ID NUMBER(6) NULL,
SEG_ID NUMBER(6) NOT NULL,
SERV_TYPE_ID NUMBER(3) NOT NULL,
PARTNER_ID NUMBER(3) NULL,
CONSTRAINT pk_TRANSP_BOOK_ID PRIMARY KEY (TRANSP_BOOK_ID),
CONSTRAINT fk_TRANSP_SEG_ID FOREIGN KEY (SEG_ID) REFERENCES TRIP_SEGMENT(SEG_ID),
CONSTRAINT fk_TRANSP_SERV_ID FOREIGN KEY (SERV_TYPE_ID) REFERENCES SERVICE_TYPE(SERV_TYPE_ID),
CONSTRAINT fk_TRANSP_PARTNER_ID FOREIGN KEY (PARTNER_ID) REFERENCES PARTNER(PARTNER_ID)
);
PARTNER:
CREATE TABLE PARTNER(
PARTNER_ID NUMBER(3) NOT NULL,
PARTNER_NAME VARCHAR(50) NOT NULL,
CONTACT_FNAME VARCHAR(20) NOT NULL,
CONTACT_LNAME VARCHAR(20) NOT NULL,
ADDRESS VARCHAR(100) NULL,
PHONE_NO NUMBER(20) NOT NULL,
EMAIL VARCHAR(50) NULL,
SERV_TYPE_ID NUMBER(3) NOT NULL,
CONSTRAINT pk_PARTNER_ID PRIMARY KEY (PARTNER_ID),
CONSTRAINT fk_PART_SERV_ID FOREIGN KEY (SERV_TYPE_ID) REFERENCES SERVICE_TYPE(SERV_TYPE_ID)
);
I wanted to create a FULL OUTER JOIN like this:
SELECT TS.SEG_ID, TS.DEPARTURE_LOCATION, TS.DESTINATION, P.PARTNER_NAME
FROM TRIP_SEGMENT TS
FULL OUTER JOIN TRANSPORTATION T
ON TS.SEG_ID = T.SEG_ID
FULL OUTER JOIN PARTNER P
ON T.PARTNER_ID = P.PARTNER_ID;
...but have it restricted to PARTNER.PARTNER_ID < 6. If I just add a WHERE clause at the end of the JOIN, this will restrict all the values to those where there is an association with PARTNER.PARTNER_ID < 6, therefore defeating the purpose of the FULL OUTER JOIN.
So far, I've come up with this solution:
First, create a table that only contains PARTNER.PARTNER_ID < 6 :
CREATE TABLE TRANSPORTATION_PARTNER AS SELECT * FROM PARTNER WHERE PARTNER_ID < 6;
Then, use that table in the FULL OUTER JOIN instead:
SELECT TS.SEG_ID, TS.DEPARTURE_LOCATION, TS.DESTINATION, TP.PARTNER_NAME
FROM TRIP_SEGMENT TS
FULL OUTER JOIN TRANSPORTATION T
ON TS.SEG_ID = T.SEG_ID
FULL OUTER JOIN TRANSPORTATION_PARTNER TP
ON T.PARTNER_ID = TP.PARTNER_ID;
This works fine and it demonstrates what I'm trying to achieve, however I was wondering if there is a way of doing in one single query AND using a subquery.
Thank you!

Answer 1

YES, just do something like :
SELECT TS.SEG_ID, TS.DEPARTURE_LOCATION, TS.DESTINATION, P.PARTNER_NAME
FROM TRIP_SEGMENT TS
FULL OUTER JOIN TRANSPORTATION T
ON TS.SEG_ID = T.SEG_ID
FULL OUTER JOIN (SELECT *
FROM PARTNER
WHERE PARTNER.PARTNER_ID < 6) P
ON T.PARTNER_ID = P.PARTNER_ID;

Answer 2

You are placing restrictions on the rows to be selected so you can use LEFT JOIN instead of the FULL OUTER JOIN. Try something like
SELECT TS.SEG_ID, TS.DEPARTURE_LOCATION, TS.DESTINATION, P.PARTNER_NAME
FROM TRIP_SEGMENT TS
FULL OUTER JOIN TRANSPORTATION T
ON TS.SEG_ID = T.SEG_ID
LEFT OUTER JOIN PARTNER P
ON T.PARTNER_ID = P.PARTNER_ID AND P.Partner_ID = 6;