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.
Why do you need Joins
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.