Need some help with an homework assignment on SQL
Problem
Find out who (first name and last name) has played the most games in the chess tournament with an ID = 41
Background information
I got a table called Games, which contains information...
game ID
tournament ID
start_time
end_time
white_pieces_player_id
black_pieces_player_id
white_result
black_result
...about all the separate chess games that have taken place in three different tournaments ....
(tournaments having ID's of 41,42 and 47)
...and the first and last names of the players are stored in a table called People....
person ID (same ID which comes up in the table 'Games' as white_pieces_player_id and
black_pieces_player_id)
first_name
last_name
...how to make a SELECT statement in SQL that would give me the answer?
sounds like you need to limit by tournamentID in your where clause, join with the people table on white_pieces_player_id and black_pieces_player_id, and use the max function on the count of white_result = win union black_result = win.
interesting problem.
what do you have so far?
hmm... responding to your comment
SELECT isik.eesnimi
FROM partii JOIN isik ON partii.valge=isik.id
WHERE turniir='41'
group by isik.eesnimi
having count(*)>4
consider using the max() function instead of the having count(*)> number
you can add the last name to the select clause if you also add it to the group by clause
sry, I only speak American. What language is this code in?
I would aggregate a join to that table to a derived table like this:
SELECT a.last_name, a.first_name, CNT(b.gamecount) totalcount
FROM players a
JOIN (select cnt(*) gamecount, a.playerid
FROM games
WHERE a.tournamentid = 47
AND (white_player_id = a.playerid OR black_player_id = a.playerid)
GROUP BY playerid
) b
ON b.playerid = a.playerid
GROUP BY last_name, first_name
ORDER BY totalcount
something like this so that you are getting both counts for their black/white play and then joining and aggregating on that.
Then, if you only want the top one, just select the TOP 1
Related
I'm currently learning SQL by working through these exercises: https://sqlzoo.net/wiki/The_JOIN_operation
I'm on Example 8 which asks: "Show the name of all players who scored a goal against Germany."
Here is what I currently have:
SELECT DISTINCT(goal.player), goal.gtime, game.team1, game.team2
FROM game JOIN goal ON (goal.matchid = game.id)
WHERE (game.team1='GER' OR game.team2='GER') AND (goal.teamid<>'GER')
I would expect that results would be returned with only unique names. However, that is not the case as we can see "Mario Balotelli" is listed twice. Why doesn't the DISTINCT command work in this instance?
Thank you!
DISTINCT operates on the record level, so you should use distinct for the whole row or if you need extra fields to show up in your result, you need to perform a GROUP BY on the player and bring along other fields by joining to the grouped result.
but i reckon the intended answer is only the player name, so query would be something like this:
SELECT DISTINCT player
FROM game JOIN goal ON matchid = id
WHERE (game.team1='GER' OR game.team2='GER') AND (goal.teamid<>'GER')
It looks like "Mario Balotelli" can have multiple goal.gtime. Or can have different contributing values from Team1 and Team2. So try removing the additional columns you have in your select clause.
DISTINCT gets the distinct rows based on all selected columns. As the goal times differ selecting that column will make the rows different (distinct) from one another.
The question only asks you to select the player's name
SELECT DISTINCT player
FROM game
JOIN goal ON matchid = id
WHERE (team1='GER' OR team2='GER')
AND (teamid <>'GER')
This link looks like it would useful further reading https://www.designcise.com/web/tutorial/what-is-the-order-of-execution-of-an-sql-query
Edit: If you want more than one column but only a distinct list of players you are in the realms of aggregation, you would min/max/sum/avg the other data for the group.
SELECT player, team1, team2, MIN(gtime) AS min_gtime, MAX(gtime) AS max_gtime, COUNT(1) AS goals_scored
FROM game
JOIN goal ON matchid = id
WHERE (team1='GER' OR team2='GER')
AND (teamid <>'GER')
GROUP BY player, team1, team2
I have 2 tables. One lists all the goals scored in the English Premier League and who scored it and the other, the squad numbers of each player in the league.
I want to do a join so that the table sums the total number of goals by player name, and then looks up the squad number of that player.
Table A [goal_scorer]
[]1
Table B [squads]
[]2
I have the SQL query below:
SELECT goal_scorer.*,sum(goal_scorer.number),squads.squad_number
FROM goal_scorer
Inner join squads on goal_scorer.name=squads.player
group by goal_scorer.name
The issue I have is that in the result, the sum of 'number' is too high and seems to include duplicate rows. For example, Aaron Lennon has scored 33 times, not 264 as shown below.
Maybe you want something like this?
SELECT goal_scorer.*, s.total, squads.squad_number
FROM goal_scorer
LEFT JOIN (
SELECT name, sum(number) as total
FROM goal_scorer
GROUP BY name
) s on s.name = goal_scorer.name
JOIN squads on goal_scorer.name=squads.player
There are other ways to do it, but here I'm using a sub-query to get the total by player. NB: Most modern SQL platforms support windowing functions to do this too.
Also, probably don't need the left on the sub-query (since we know there will always be at least one name), but I put it in case your actual use case is more complicated.
Can you try this if you are using sql-server?
select *
from squads
outer apply(
selecr sum(goal_scorer.number) as score
from goal_scorer where goal_scorer.name=squads.player
)x
For the sake of example, let's say I have the following models:
teams
each team has an arbitrary amount of fans
In SQL, this means you end up with the following tables:
team: identifier, name
fan: identifier, name
team_fan: team_identifier, fan_identifier
I am looking for an approach to retrieve:
all teams, and
for each team, the first 5 fans of which his/her name starts with an 'A'.
What is an efficient approach to do this?
In my current naive approach, I do <# teams> + 1 queries, which is troublesome:
First: SELECT * FROM team
Then, for each team with identifier X:
SELECT *
FROM fan
INNER JOIN team_fan
ON fan.identifier = team_fan.fan_identifier AND team_fan.team_identifier = X
WHERE fan.name LIKE 'A%'
ORDER BY fan.name LIMIT 5
There should be a better way to do this.
I could first retrieve all teams, as I do now, and then do something like:
SELECT *
FROM fan
WHERE fan.name LIKE 'A%'
AND fan.identifier IN (
SELECT fan_identifier
FROM team_fan
WHERE team_identifier IN (<all team identifiers from first query>))
ORDER BY fan.name
However, this approach ignores the requirement that I need the first 5 fans for each team with his/her name starting with an 'A'. Just adding LIMIT 5 to the query above is not correct.
Also, with this approach, if I have a large amount of teams, I am sending the corresponding team identifiers back to the database in the second query (for the IN (<all team identifiers from first query>)), which might kill performance?
I am developing against PostgreSQL, Java, Spring and plain JDBC.
You need a three table join
SELECT team.*, fan.*
FROM team
JOIN team_fan
ON team.team_identifier = team_fan.team_identifier
JOIN fan
ON fan.fan_identifier = team_fan.fan_identifier
Now to filter you need to do this.
with cte as (
SELECT team.*, fan.*,
row_number() over (partition by team.team_identifier
order by fan.name) as rn
FROM team
JOIN team_fan
ON team.team_identifier = team_fan.team_identifier
JOIN fan
ON fan.fan_identifier = team_fan.fan_identifier
WHERE fan.name LIKE 'A%'
)
SELECT *
FROM cte
WHERE rn <= 5
Usually, RDBMSes have their own hacks around standard SQL that allows you to have a number in a count over some condition of grouping/ordering.
Postgres is no exception, it got ROW_NUMBER() function.
What you need is to partition your row numbers properly, order them by alphabet and restrict the query to row numbers < 6.
I have two tables:
The first one (players) contains player records with it ID's and names.
Another one (results) contains results:
ID of 1 player against ID of 2 player
How can I select their names?
SELECT *
FROM results
ORDER by result_date DESC
It looks like this for now. I want to have instead of numbers real player names.
You just need to set two different alias for the players table:
select *
from results
join players as pair1players on results.Pair1 = pair1players.ID
join players as pair2players on results.Pair2 = pair2players.ID
order by result_date desc
Here, supposing Pair1 is the name of the field "Pair #1" you showed in the screenshot, and Pair2 is the name of the field "Pair #2".
This could help:
SELECT players.ID, players.Name
FROM players
INNER JOIN results ON players.ID=results.playersID
I am now creating a reporting service with visual business intelligent.
i try to count how many users have been created under an org_id.
but the report consist of multiple org_id. and i have difficulties on counting how many has been created under that particular org_id.
TBL_USER
USER_ID
0001122
0001234
ABC9999
DEF4545
DEF7676
TBL_ORG
ORG_ID
000
ABC
DEF
EXPECTED OUTPUT
TBL_RESULT
USER_CREATED
000 - 2
ABC - 1
DEF - 2
in my understanding, i need nested SELECT, but so far i have come to nothing.
SELECT COUNT(TBL_USER.USER_ID) AS Expr1
FROM TBL_USER INNER JOIN TBL_ORG
WHERE TBL_USER.USER_ID LIKE 'TBL_ORG.ORG_ID%')
this is totally wrong. but i hope it might give us clue.
It looks like the USER_ID value is the concatenation of your ORG_ID and something to make it unique. I'm assuming this is from a COTS product and nothing a human would have built.
Your desire is to find out how many entries there are by department. In SQL, when you read the word by in a requirement, that implies grouping. The action you want to take is to get a count and the reserved word for that is COUNT. Unless you need something out of the TBL_ORG, I see no need to join to it
SELECT
LEFT(T.USER_ID, 3) AS USER_CREATED
, COUNT(1) AS GroupCount
FROM
TBL_USER AS T
GROUP BY
LEFT(T.USER_ID, 3)
Anything that isn't in an aggregate (COUNT, SUM, AVG, etc) must be in your GROUP BY.
SQLFiddle
I updated the fiddle to also show how you could link to TBL_ORG if you need an element from the row in that table.
-- Need to have the friendly name for an org
-- Now we need to do the join
SELECT
LEFT(T.USER_ID, 3) AS USER_CREATED
, O.SOMETHING_ELSE
, COUNT(1) AS GroupCount
FROM
TBL_USER AS T
-- inner join assumes there will always be a match
INNER JOIN
TBL_ORG AS O
-- Using a function on a column is a performance killer
ON O.ORG_ID = LEFT(T.USER_ID, 3)
GROUP BY
LEFT(T.USER_ID, 3)
, O.SOMETHING_ELSE;