Doubt Regarding LEFT JOIN Operation

Question

Hello,
With the Old syntax in place it is easier for find that which join is performed on which table ...
But with the new syntax ..m getting bit confused when INNER & LEFT JOINS used together ...
Below is the FROM clause ...please explain .. how this JOIN is gonna take place ..& which table is Left joined with whom...
FROM VW_TRANS_MANAGER_SALES ref_1
LEFT OUTER JOIN VW_AGREE_ASSIGN_TAG_DTLS ass
ON Trim(ass.agreement_id) = trim(ref_1.AGREEMENT_ID)
LEFT OUTER JOIN VW_CURENT_RATING_DTLS CURR
ON (ref_1.company_code =curr.COMPANYCODE)
LEFT OUTER JOIN VW_PREV_RATING_DETAILS PREV
ON (ref_1.company_code =prev.COMPANYCODE)
LEFT OUTER JOIN CRMADMIN.CO_MA_COMPANY_CONTACTS cont
ON (ref_1.CLIENT_CONTACT_ID= cont.CONTACT_ID)
LEFT OUTER JOIN CRMADMIN.COR_CRM_MST_CITY city
ON (city.City_id= cont.City_id))
---------------------------------------------------------------------------------------------------------------------------------------

Answer 1

Hi,
Aijaz Mallick wrote:
Yeah .. but was a bit Confusing as u used 2 columns in each table....
Doesn't it depends on the joining condition we use ... lets Say ..if i use an INNER join after 2 LEFT join ... & m doing an that inner join with the first SOURCE table .... then will it perform a join on the resultset on the previous Joins...???Sorry, I'm not sure what you're asking.
Please post a specific example of a join that you don't understand, or some results that you don't know how to get.
Use commonly available tables (like those in the scott or hr schemas) or post your own CREATE TABLE and INSERT statements.
Using ANSI syntax, the results are as if the joins were done in the order they appear in the FROM clause (even though the optimizer may not actually do them in that order).
For example, in the querry below, the inner-join between emp and salgrade is done first, then the outer join with dept is done to that result set.
SELECT     d.dname
,     e.ename
,     g.losal
FROM          scott.emp     e
JOIN          scott.salgrade     g     ON     e.sal     BETWEEN     g.losal
                                   AND     g.hisal
RIGHT OUTER JOIN  scott.dept     d     ON     e.deptno     = d.deptno
;Output:
DNAME          ENAME           LOSAL
ACCOUNTING     CLARK            2001
ACCOUNTING     MILLER           1201
ACCOUNTING     KING             3001
RESEARCH       FORD             2001
RESEARCH       SCOTT            2001
RESEARCH       JONES            2001
RESEARCH       ADAMS             700
RESEARCH       SMITH             700
SALES          BLAKE            2001
SALES          ALLEN            1401
SALES          MARTIN           1201
SALES          WARD             1201
SALES          JAMES             700
SALES          TURNER           1401
OPERATIONSNotice that the OPERATIONS department, which has no matches in the other tables, is still included because of the outer join.
If you want to have the joins done in a different order, you can explicitly join some table first, either in a sub-query or just by grouping joins within parentheses in the same FROM clause, as in the query below (which produces the same results as the query above):
SELECT     d.dname
,     e.ename
,     g.losal
FROM          scott.dept     d
LEFT OUTER JOIN     (     -- Join the following tables first:
               scott.emp     e
          JOIN     scott.salgrade     g     ON     e.sal     BETWEEN     g.losal
                                        AND     g.hisal
          )     ON     d.deptno     = e.deptno
;