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Theta Join

 
Amandeep Singh
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I am unable to makeout the meaning of theta join. To me there seems no difference between theta join and inner join.
 
Arun Kumar Gupta
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Theta join is the join when two entities are joined not on the relationship exist between them but explicitly specifying some other field.

Select b
from b.item,c.categories
where b.(something other than relationship)=c.(something)

Inner join is the join on relationship entities and no need to sepecify the join in =,only the matching entities are there that exist in both the entities

select b
from b.item INNER JOIN c.categoreis

Outer join when you want all the field of one side to exist whether match is found or not LEFT ,RIGHT,

Correct me if i am wrong
 
Amandeep Singh
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Thanks...

even if there is no relationship between the comparing the field's, it dosen't matter, the same thing we are doing in inner join.

i am again confused here for the differnce between theta join and inner join.

i thibk it would be best to give a sql query for theta join and inner join. Then highlight the differnce between them.
 
Chaminda Amarasinghe
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Inner Join:
based on database relationship. apply existing pk, fk relationship. you no need to specify how to join

Theta join:
the relationship is made by you explicitly. no primary key foreign key relationship in db level. so you have to explicitly specify fields used to define relationship.
 
Amandeep Singh
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Chaminda, i am unable to understand, can you give example.
 
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