Test by Bikram | Databases | Test 1 | Question: 6

Question

In SQL the statement

→ Select * from R ,S 

  is equivalent to:

• A.

  select * from R natural join S
  

• B.

  select * from R inner join S
  

• C.

  select * from R cross join S
  

• D.

  select * from R union join S
  

Answer 1

IN given sql statement no condition is mentioned....so it displays all possible rows m*n.

- in inner join we generally use a condition like "table1.attributes (operator) table2.attributes" [here operator can be any valid one]

-in equijoin it is similar to innerjoin like above but here operator we use is only equality operator(=) and not any else between the attributes.

-in natural join you no need to mention equality condition also as it is implicitly understood....

so,

JOIN+NO CONDITION = CROSS-JOIN

JOIN+EQUALITY CONDITION = EQUI-JOIN

JOIN+ANY VALID CONDITION = INNER-JOIN