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Oracle: Compare SQL subqueries
One of the
problems with SQL is that the same query can be
expressed in a variety of ways, all with
identical results but widely varying execution
plans and readability. In the example below,
the following three SQL queries all produce the
same output, but they look quite different.
Each of the below queries produces a list of
books that have no sales. Here is the output:
BOOK_TITLE
----------------------------------------
was george washington
gay?
cooking
light
never eat
boogers
how to housebreak your horse
Your
assignment is as follows:
-
Copy
these query and run it against the pubs
database to verify that the same results
are returned.
-
Once
the output is confirmed, investigate
each for of the subquery with a Google
search and a review of Chapter 19.
-
Write a
300 word paper outlining your
conclusions about the most efficient way
to get the desired output and your
recommendations on the most efficient
and readable way to code this SQL query.
column book_title format a40
-- FORM 1
select
book_title
from
book
where
book_title not in (
select
distinct
book_title
from
book,
sales
where
book.book_key =
sales.book_key
and
quantity > 0);
-- FORM 2
select
book_title
from
book
where
book_key not in (select book_key from
sales);
-- FORM 3
select
book_title,
nvl(quantity,0)
from
book t,
sales s
where
t.book_key = s.book_key(+)
and
quantity is null
;
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