Rewriting simple query using EXISTS, IN, ALL, ANY operators

Question

I have the following tables: Ships (Name is PK)

Name	Class	Launching_year
Kongo	Kongo	1912
Haruna	Kongo	1913
Evstafi	Evstafi	1906

Consequences ((Ship, Battle) is UK, ship is FK to Ships table)

Ship	Battle	Result
Kongo	Midway Battle	unharmed
Haruna	Guadalcanal Campaign	unharmed
Evstafi	Battle from Cape Sarych	unharmed

I have to find the name of those ships that participated in the battles in which ships from the Kongo class participated. I have to use a subquery and EXISTS, IN, ALL or ANY operators and I can't use aggregate functions (COUNT, SUM, MAX, MIN, etc). I'm using Oracle DB.

I can find the answer with the following query(version1):

SELECT s.name
FROM ships s JOIN consequences c ON (s.name = c.ship)
WHERE s.class = 'Kongo' AND c.battle IS NOT NULL;

Returning: Kongo, Haruna

I managed to rewrite the code in the following way(version2):

SELECT name
FROM ships
WHERE name IN (SELECT s.name
               FROM ships s JOIN consequences c ON (s.name = c.ship)
               WHERE s.class = 'Kongo' AND c.battle IS NOT NULL)

The query returns the same results. I'm not satisfied with this solution, because the only thing I did was placing version 1 as a subquery in version 2, where once again I'm selecting the name of the ships.

I was wondering if there are other more elegant solutions to this problem.

Answer 1

With your sample data:

WITH
    ships AS
        (
            Select 'Kongo'   "NAME", 'Kongo'   "CLASS", 1912 "LAUNCH_YEAR" From Dual Union All
            Select 'Haruna'  "NAME", 'Kongo'   "CLASS", 1913 "LAUNCH_YEAR" From Dual Union All
            Select 'Evstafi' "NAME", 'Evstafi' "CLASS", 1906 "LAUNCH_YEAR" From Dual 
        ),
    consequences AS
        (
            Select 'Kongo'   "SHIP", 'Midway Battle'            "BATTLE", 'unharmed' "RESULT" From Dual Union All
            Select 'Haruna'  "SHIP", 'Guadalcanal Campaign'     "BATTLE", 'unharmed' "RESULT" From Dual Union All
            Select 'Evstafi' "SHIP", 'Battle from Cape Sarych'  "BATTLE", 'unharmed' "RESULT" From Dual 
        )

... using EXISTS (subquery)

Select  c.SHIP
From    consequences c
Where   EXISTS (Select NAME From ships where NAME = c.SHIP And CLASS = 'Kongo')

--  SHIP  
--  -------
--  Kongo   
--  Haruna

... using IN (subquery)

Select  s.NAME 
From    ships s
Where   s.CLASS = 'Kongo' And
        s.NAME IN(Select SHIP From consequences where SHIP = s.NAME)

--  NAME  
--  -------
--  Kongo   
--  Haruna 

... using ANY (subquery)

Select  c.SHIP
From    consequences c
Where   c.SHIP = ANY (Select NAME From ships where NAME = c.SHIP And CLASS = 'Kongo')    

--  SHIP  
--  -------
--  Kongo   
--  Haruna