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Home >> Interview Question >> Sql Server >> Post New Question Subscribe to Interview Questions

What is mean by JOIN and Types of JOIN?

Posted By :Narayanan     Posted Date :August 31, 2011    Points :40   Category :Sql Server 
Used in an SQL statement to query data from two or more tables, based on a relationship between certain columns in these tables.
Types of JOIN:
JOIN: Return rows when there is at least one match in both tables
LEFT JOIN: Return all rows from the left table, even if there are no matches in the right table
RIGHT JOIN: Return all rows from the right table, even if there are no matches in the left table
FULL JOIN: Return rows when there is a match in one of the tables


You can also find related Interview Question to What is mean by JOIN and Types of JOIN?  below: 

What are different Types of Join?

  

Cross Join

A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.

Inner Join

A join that displays only the rows that have a match in both joined tables is known as inner Join. This is the default type of join in the Query and View Designer.

Outer Join

A join that includes rows even if they do not have related rows in the joined table is an Outer Join. You can create three different outer join to specify the unmatched rows to be included:

. Left Outer Join: In Left Outer Join all rows in the first-named table i.e. "left" table, which appears leftmost in the JOIN clause are included. Unmatched rows in the right table do not appear.
. Right Outer Join: In Right Outer Join all rows in the second-named table i.e. "right" table, which appears rightmost in the JOIN clause are included. Unmatched rows in the left table are not included.
. Full Outer Join: In Full Outer Join all rows in all joined tables are included, whether they are matched or not.

Self Join

This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company has a hierarchal reporting structure whereby one member of staff reports to another. Self Join can be Outer Join or Inner Join.
(More...)

What is Thread.Join() in threading ?

  
There are two versions of Thread.Join :-
. Thread.join().
. Thread.join(Integer) this returns a Boolean value.
The Thread.Join method is useful for determining if a thread has completed before starting another task. The Join method waits a specified amount of time for a thread to end. If the thread ends before the time-out, Join returns true; otherwise it returns False. Once you call Join, the calling procedure stops and waits for the thread to signal that it is done.
Example you have "Thread1" and "Thread2" and while executing 'Thread1" you call "Thread2.Join()".So "Thread1" will wait until "Thread2" has completed its execution and the again invoke "Thread1".
Thread.Join(Integer) ensures that threads do not wait for a long time. If it exceeds a specific time which is provided in integer the waiting thread will start. (More...)

How do I invite users to join a Windows SharePoint Services Site? Is the site secure?

  
SharePoint-based Web sites can be password-protected to restrict access to registered users, who are invited to join via e-mail. In addition, the site administrator can restrict certain members' roles by assigning different permission levels to view post and edit. (More...)

What is a Join in SQL Server?

  
Join puts data from two or more tables into a single result set. (More...)

How do we join the values in an array?

  
Using the method Join() as follows.

var arr = new Array();
arr = ["one","two","three","four"];
alert(arr.join(",")); (More...)

what is left outer join?

  

Matched records from the tables and unmatched records from left table. (More...)

Get data from 2 tables using join?

  
Select s.name,s.code,m.eng,m.math from Student S INNER Join Marks m on s.RollNo=m.RollNo; (More...)

Performance wise which one is the best? IN,EXISTS or INNER JOIN

  
It depends.

Generally speaking JOINs are much better than EXISTS & EXISTS is better than IN, performance wise.

If your result set is small then you can use IN or EXISTS.

But if result set contains a large set of records, then use JOINS.


(More...)

What is Inner Join?

  
return rows when there is at least one match in both tables. (More...)

What is Self Join?

  
To join within that table is called self join.

Example to check Duplicate Records:

select empid from employee where empid not in(select empid from employee group by empid having count(*)>1)

select empid a ,empname b from emp a, emp b
where a.empid=b.empid

Regards

sriram.R (More...)

How do I invite users to join a Windows SharePoint Services Site?
Is the site secure?

  
SharePoint-based Web sites can be password-protected to restrict access to registered users, who are invited to join via e-mail. In addition, the site administrator can restrict certain members' roles by assigning different permission levels to view post and edit. (More...)


How do I invite users to join a Windows SharePoint Services Site? Is the site secure?

  

SharePoint-based Web sites can be password-protected to restrict access to registered users, who are invited to join via e-mail. In addition, the site administrator can restrict certain members' roles by assigning different permission levels to view post and edit.

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