How to Include Zero in a COUNT() Aggregate? - sql

Question

I have three tables, and I join them and use where Group by - count, I could not get the countries with zero results in the output. I am still lost.
Here is the SQLfiddle
http://sqlfiddle.com/#!4/e330ec/7
CURRENT OUTPUT
(UKD) 3
(EUR) 2
(USA) 2
(CHE) 1
EXPECTED OUTPUT
(UKD) 3
(EUR) 2
(IND) 0
(LAO) 0
(USA) 2
(CHE) 1

Answer 1

You can use a RIGHT JOIN as suggested in another answer or you can reorder your joins and use a LEFT JOIN:
SELECT
C.COUNTRY_CODE,
COUNT(GAME_TYPE)
FROM
COUNTRY_TABLE C
LEFT JOIN PLAYER_TABLE P ON P.COUNTRY_ID = C.COUNTRY_ID
LEFT JOIN PLAYER_GAME_TYPE G ON P.PLAYER_ID = G.PLAYER_ID
WHERE
G.GAME_TYPE = 'GOLF'
OR G.GAME_TYPE IS NULL
GROUP BY
C.COUNTRY_CODE;
Note the inclusion of OR G.GAME_TYPE IS NULL in the WHERE clause -- if you only have G.GAME_TYPE = 'GOLF', then desired results will be filtered out after the joins.

Answer 2

You can prefer applying the following steps as an option :
convert second LEFT JOIN to RIGHT JOIN(since desired missing abbreviations are in COUNTRY_TABLE which stays at right)
make the filtering condition(followed by the WHERE clause) G.GAME_TYPE = 'GOLF' a match condition
by taking next to the ON clause
such as
SELECT C.COUNTRY_CODE, COUNT(GAME_TYPE)
FROM PLAYER_TABLE P
LEFT JOIN PLAYER_GAME_TYPE G
ON P.PLAYER_ID = G.PLAYER_ID
RIGHT JOIN COUNTRY_TABLE C
ON P.COUNTRY_ID = C.COUNTRY_ID
AND G.GAME_TYPE = 'GOLF'
GROUP BY C.COUNTRY_CODE;
Demo

Answer 3

The simple change of tables join order can solve the problem
SELECT C.COUNTRY_CODE, COUNT(GAME_TYPE)
FROM COUNTRY_TABLE C -- get all countries
LEFT JOIN PLAYER_TABLE P ON P.COUNTRY_ID = C.COUNTRY_ID -- join all players
LEFT JOIN PLAYER_GAME_TYPE G ON P.PLAYER_ID = G.PLAYER_ID AND G.GAME_TYPE = 'GOLF' -- join only GOLF games
GROUP BY C.COUNTRY_CODE;
sqlize online

Answer 4

This is your query:
SELECT C.COUNTRY_CODE, COUNT(GAME_TYPE)
FROM PLAYER_TABLE P
LEFT JOIN PLAYER_GAME_TYPE G ON P.PLAYER_ID = G.PLAYER_ID
LEFT JOIN COUNTRY_TABLE C ON P.COUNTRY_ID = C.COUNTRY_ID
WHERE G.GAME_TYPE = 'GOLF'
GROUP BY C.COUNTRY_CODE;
This query seems to try to select all players even when they are no golfers. This doesn't work, however, as WHERE G.GAME_TYPE = 'GOLF' removes all outer joined rows, so you end up with an inner join (all players who play golf.) At last you outer join the countries table, which would give you players that don't belong to a country. Is this indented? I don't think so.
What you want is countries, so select from countries. Then properly outer join players and types in order to count them.
SELECT c.country_code, COUNT(g.game_type) as golfers_in_country
FROM country_table c
LEFT JOIN player_table p ON p.country_id = c.country_id
LEFT JOIN player_game_type g ON g.player_id = p.player_id AND g.game_type = 'GOLF'
GROUP BY c.country_code
ORDER BY c.country_code;
You can use a CTE to get this more readable. It is longer, but makes the intention crystal-clear. Structuring one's queries like this helps avoiding mistakes.
WITH golfers AS
(
SELECT *
FROM player_table
WHERE player_id IN
(
SELECT player_id
FROM player_game_type
WHERE game_type = 'GOLF'
)
)
SELECT c.country_code, COUNT(g.player_id) as golfers_in_country
FROM country_table c
LEFT JOIN golfers g ON g.country_id = c.country_id
GROUP BY c.country_code
ORDER BY c.country_code;