Question { L&T, 30620 }

What is a view? is View updatable?

Answer

view is a virtual table , which provides to a subset of columns from one or more tables. in which doesn't have its own data.
yes view is updatbable in a single update statement

Question { Polaris, 14878 }

what are the joins,primary key,foriegn key, candidate key,
super key and expain them?

Answer

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.