What
is a SQL Join? When would you use Joins?
Join is used to fetch data rows from more than
one tables simultaneously based on your join conditions.
Types
of joins in SQL:-
1.
INNER JOIN
2.
OUTER JOIN
3.
SELF JOIN
4.
CROSS JOIN
5.
MULTIPLE JOIN
All the Joins are work between the table’s key relations.
What
is inner join in SQL? when would you use it?
Inner Join returns the matched rows from both the
tables. If both the keys are matched then return rows otherwise not!
What
is Left Outer Join in SQL? when would you use it?
In the LEFT OUTER JOIN, returns all the matched rows
from the left table and matched rows from right table. If the right table is not
matched then will return NULL values.
What
is Right Outer Join
in SQL? when would you use it?
In the RIGHT OUTER JOIN, returns all the matched rows
from the right table and matched rows from left table. If the left table rows
are not matched then return NULL values.
What
is Full Outer Join
in SQL? when would you use it?
FULL OUTER JOIN work between with both the LEFT
OUTER and RIGHT OUTER JOINS. If the condition is matched then returns matched
rows otherwise returns NULL values.
What
is SELF JOIN and when would you use it?
A SELF JOIN is join which is used to join a table
to itself.
There is no SELF JOIN keyword and it is used to
compare values in a column with other values in the same column in the same
table.
For example,
SELECT * FROM TableA t1, TableA t2
WHERE t1.Id = t2.Id
In the above query, WHERE clause could be any
given expression as per you!
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