Why and how to use SQL DISTINCT Clause?

Question

Abhishek Srivasatava · Answer

Distinct is used when unique result is needed from user side. It is used because after joining many tables there is chance of multiple rows for single data may come.For examplePrsn table holding the Adhar number of person.And we join this prsn table with prsn_buy_prod table. Let person buy 3 product so three rows will exist.
Program without distinct:
SELECT A.PRSN_ADHAR_NUMFROM ADHAR ALEFT JOIN PRSN_BUY_PROD BON A.PRSN_ADHAR_NUMNUM=B.PRSN_ADHAR_NUM_NUM Where A.name= ‘P Raturi’ 
Output :
987456321987456321987456321
For the above program 3
rows will come for the single name P Raturi.
But if use distinct along with select statement in the above program then single record will come.and  
SELECT DISTICT A.PRSN_ADHAR_NUMFROM ADHAR ALEFT JOIN PRSN_BUY_PROD BON A.PRSN_ADHAR_NUMNUM=B.PRSN_ADHAR_NUM_NUM Where A.name= ‘P Raturi’
Output :987456321

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Why and how to use SQL DISTINCT Clause?

Abhishek Srivasatava

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