joins sql questions code example

Example 1: joins in sql

INNER JOIN:
is used when retrieving data from multiple
tables and will return only matching data.

LEFT OUTER JOIN:
is used when retrieving data from
multiple tables and will return
left table and any matching right table records.

RIGHT OUTER JOIN:
is used when retrieving data from
multiple tables and will return right
table and any matching left table records

FULL OUTER JOIN:
is used when retrieving data from
multiple tables and will return both
table records, matching and non-matching.



INNER JOIN :
SELECT select_list From TableA A
Inner Join TableB B
On A.Key = B.Key


LEFT OUTER JOIN :
SELECT select_list From TableA A
Left Join TableB B
On A.Key = B.Key

(where b.key is null)//For delete matching data



RIGTH OUTER JOIN :
SELECT select_list From TableA A
Right Join TableB B
On A.Key = B.Key


FULL JOIN :
SELECT select_list From TableA A
FULL OUTER Join TableB B
On A.Key = B.Key

Example 2: 3 joins in sql

SELECT e.FIRST_NAME ,     -- coming from EMPLOYEES table
			 d.DEPARTMENT_NAME ,-- coming from DEPARTMENTS table
			 l.CITY ,           -- coming from LOCATIONS table
			 c.COUNTRY_NAME ,   -- coming from COUNTRIES table
			 r.REGION_NAME      -- coming from REGIONS table
FROM EMPLOYEES e 
	INNER JOIN DEPARTMENTS d on e.DEPARTMENT_ID = d.DEPARTMENT_ID
	INNER JOIN LOCATIONS l   on l.LOCATION_ID   = d.LOCATION_ID
	INNER JOIN COUNTRIES c   on l.COUNTRY_ID    = c.COUNTRY_ID
	INNER JOIN REGIONS r     on c.REGION_ID     = r.REGION_ID ;