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SQL Server Self Joins

Posted on 2014-11-19
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Last Modified: 2014-11-20
Hi,

I have a table called Test with columns questionid,text,qid

basically qid also a questionid which is a help text for the main question. questions
which does not have help text will have qid as NULL

now i want to retrive all questionid's with the question text but those questions which has
qid I want that text for qid in the same row . so basically I want the question text and the  qid
text (help text) in the same row for each questionid. for those questions where qid is null should return null. and I dont want the qid questionid's appearing as seperate questions in my result sets.

Example

questinid   text                         qid
101         what is ur name ?     102
102         this is mandatory       null
103         DOB                             null

so my result set should be like below :

questionid   text                        helptext
101          What is ur name ?    this is mandatory
103          DOB                           null



can some one please advise me the best query for this ?

Many Thanks
0
Comment
Question by:gvamsimba
  • 2
4 Comments
 
LVL 47

Accepted Solution

by:
Vitor Montalvão earned 350 total points
ID: 40451988
Try this one:
SELECT T1.questinid, T1.text, T2.text helptext
FROM Test T1
LEFT OUTER JOIN Test T2 ON T1.qid=T2.questinid
WHERE NOT EXISTS (SELECT 1 FROM Test T3 WHERE T1.questinid=T3.qid)

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0
 
LVL 11

Assisted Solution

by:John_Vidmar
John_Vidmar earned 150 total points
ID: 40453796
Similar solution to Vitor, but eliminates the correlated sub-query:
SELECT	T1.questinid
,	T1.text
,	T2.text helptext
FROM	Test T1
LEFT
JOIN	Test T2			ON	T1.qid = T2.questinid
LEFT
JOIN	Test T3			ON	T1.qid = T3.questinid
WHERE	T3.questinid IS NULL

Open in new window

0
 

Author Comment

by:gvamsimba
ID: 40454687
Hi John , your join condition on t3 is incorrect. the below will work...


SELECT      T1.questinid
,      T1.text
,      T2.text helptext
FROM      Test T1
LEFT
JOIN      Test T2                  ON      T1.qid = T2.questinid
LEFT
JOIN      Test T3                  ON      T1.questinid = T3.qid
WHERE      T3.questinid IS NULL
0
 

Author Closing Comment

by:gvamsimba
ID: 40454691
Excellent
0

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