Joins is a one of the key concept in SQL. In an RDBMS we have tables with one-one, one-many and many-many relationships.
So the concept of RDBMS depends on relationship.
In a realtime environment database architect will design relation between various tables. User needs collective data from all the related tables.
Joins are much useful.
FULL OUTER JOIN
LEFT OUTER JOIN
RIGHT OUTER JOIN
FOJ: It retrieves rows from all the tables
LOJ: It retrieves all rows from left table and also matching rows of the two tables
ROJ:It retrieves all rows from right table and also matching rows of the two tables
Note: OUTER is Optional word
In my next post I will add some examples on this.