Question

Which of the following is a valid SQL statement?

Answer 1

Answer:

Hi!

The correct answer is B.

Explanation:

This sentence SELECT * FROM customers JOIN orders ON (customer#) selects all the columns of both customers and orders and joins by the name of the column customer.

A and B options have syntactic problems:  

• A and C: Same alias name for multiple tables.

• A and C: Selected columns are ambiguous.

• C: refers to an alias not declared on the FROM sentence.

a) SELECT c.customer#, order#, orderdate, shipdate(omits aliases) FROM customers c NATURAL JOIN orders c(same aliases definiton);

c) SELECT c.customer#, order#, orderdate, shipdate(omits aliases) FROM customers c, orders c(same aliases definiton) WHERE c.customer# = o.customer#(o not declared);