what are the joins,primary key,foriegn key, candidate key,
super key and expain them?
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Answer Posted / vikash kr pandey
1> JOIN:- JOIN IS USED TO VIEW AND RETRIEVE DATA FROM MULTIPLE TABLE OR RELATED TABLES IN A SINGLE RESULT SET.
2> PRIMARY KEY:-PRIMARY KEY IS A SET OF COLUMNS WHOSE VALUES UNIQUELY IDENTIFY ALL THE ROWS IN A TABLE AND CAN NOT CONTAIN NULL VALUES.
3> FORIEGN KEY:-A COLUMN IN ONE TABLE WHOSE VALUES MATCH THE PRIMARY KEY IN SOME OTHER TABLE IS CALLED A FORIEGN KEY.
4> CANDIDATE KEY:-ANY ATTRIBUTE THAT IS UNIQUELY IDENTIFIES A ROW IN A TABLE IS A CANDIDATE FOR THE PRIMARY KEY. THIS TYPE OF ATTRIBUTE IS CALLED CANDIDATE KEY.
5> SUPER KEY:-THE SUPERTYPE IS DESCRIBED BY ATTRIBUTES THAT BELONGS TO ALL SUBTYPES AND CONNECTED TO THE RELATIONSHIP WITH A LINE CONTAINING A CROSSBAR.
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