how to write seff join query for my retquirement

Question

4.00/5 (1 vote)

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I create table

SQL

create table mytable1
(
  id int,
  name varchar(20),
  mid varchar(20)
)

SQL

insert into mytable1 values(1,'A',Null)
insert into mytable1 values(2,'B',1)
insert into mytable1 values(3,'C',Null)
insert into mytable1 values(4,'D',1)

id name mid
===========
1   A    null
2   B     1
3   C    null
4   D     1

I need to write the query using self join to get the following output

VB

 name mid
===========
  A    null
  B     A
  C    null
  D     A

Posted 13-Jan-13 19:30pm

Basheer Belgod

Updated 13-Jan-13 19:52pm

Tharaka MTR

v2

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Manoj Kumar Choubey · Answer 1 · 2013-01-14T02:31:00

Solution 3

SQL

Select
X.name,Y.name as name
From mytable1 X
Left Join mytable1 Y on (X.id = Y.mid)

Posted 14-Jan-13 2:31am

Manoj Kumar Choubey

Tharaka MTR · Answer 2 · 2013-01-13T19:51:00

Solution 1

try this

SQL

SELECT a.name, B.name as mid FROM mytable1 A
LEFT OUTER JOIN
(SELECT Id,name FROM mytable1 WHERE mid is null)  B
ON A.mid=B.id

Posted 13-Jan-13 19:51pm

Tharaka MTR

Updated 13-Jan-13 20:24pm

v2

Jibesh · Answer 3 · 2013-01-13T20:01:00

Solution 2

since you pass mid as integer values if you change your data type of mid to int, query execution will be faster.
following sample is based on mid as int

SQL

select e.name as Name,m.name as MID from mytable1 as e
left outer join mytable1 as
m on m.id = e.mid;

Posted 13-Jan-13 20:01pm

Jibesh

Comments

Basheer Belgod 14-Jan-13 2:28am

Thank you :) its working fine but the requirement is have to use the self join
instead of left outer join

Jibesh 14-Jan-13 2:36am

was this a homework? whether the answer is yes or no you should start reading some sql basics before you go further. The term 'self join' means table which joins self, there is no such keyword SELF JOIN like LEFT/RIGHT join.

SQL Joins tutorialsLink will help you to understand more about SQL Joins.

[no name] 14-Jan-13 9:14am

Yes I agree to jibesh. Please use once to your own knowledge using google. Google is the best friend indeed... :D