How to iterate through a select within another select - sql

Question

I have two tables Players(Name,Surname,Goals,TeamID) and Teams(Name,TeamID).
In the following query I get the average goals' number per team and select the players who have a number of goals greater than the average.
SELECT Players.Name, Players.Surname, Teams.Name, Players.Goals, (SELECT ROUND(AVG(Players.Goals)) FROM Players GROUP BY Players.TeamID) AS TeamAverage
FROM Players
JOIN Teams ON Players.TeamID = Teams.TeamID
WHERE Players.Goals > (SELECT ROUND(AVG(Players.Goals))
FROM Players
GROUP BY Players.TeamID)
In the TeamAverage column I want to display the average goals' number per team, but the query only gets the average number of goals for the first team.
Who can I iterate through this select
(SELECT ROUND(AVG(Players.Goals)) FROM Players GROUP BY Players.TeamID)
and get each result according to the teams' ID?

Answer 1

Try this, I'd personally have gone down the route of using a temp table but this should also work for you. I gave your main tables an alias of P and T to help your sub query know what to compare against:
SELECT
P.Name,
P.Surname,
T.Name,
P.Goals,
(SELECT ROUND(AVG(Players.Goals)) FROM Players WHERE Players.TeamID = P.TeamID) AS TeamAverage
FROM
Players P
JOIN Teams T ON P.TeamID = T.TeamID
WHERE
P.Goals > (SELECT ROUND(AVG(Players.Goals))
FROM Players
WHERE Players.TeamID = P.TeamID)

Answer 2

By using the query in the parentheses you are creating a sub query that gets evaluated first and independently from the row in every row. If this is not part of a view and a query that needs to be run as part of a data collection or visualization, then a temp table would work fine by itself or in a stored procedure. If it needs to be in a view, then using a join into a subquery would work.
Using a temp table:
SELECT Players.TeamID as TeamID
,ROUND(AVG(Players.Goals)) as PlayerAverage
INTO #temp
FROM Players
Group BY Players.TeamID
SELECT tea.Players.Name
,tea.Players.Surname
,tea.Teams.Name
,tea.Players.Goals
,t.PlayerAverage
FROM Players
JOIN Teams tea ON Players.TeamID = Teams.TeamID
left join #temp t on Players.TeamID = t.TeamID
WHERE Players.Goals > t.PlayerAverage
using a joined subquery:
SELECT tea.Players.Name
,tea.Players.Surname
,tea.Teams.Name
,tea.Players.Goals
,t.PlayerAverage
FROM Players
JOIN Teams tea ON Players.TeamID = Teams.TeamID
left join (SELECT Players.TeamID as TeamID
,ROUND(AVG(Players.Goals)) as PlayerAverage
FROM Players
Group BY Players.TeamID) t on Players.TeamID = t.TeamID
WHERE Players.Goals > t.PlayerAverage
Hope this helps!

Answer 3

You could do something like this using a temp table to help store the results for teamAverage
CREATE TABLE #players (
goals INT,
NAME NVARCHAR(200),
surname NVARCHAR(200),
teamid INT
)
CREATE TABLE #teams (
NAME NVARCHAR(200),
teamid INT
)
INSERT INTO #teams (
NAME,
teamid
)
VALUES
('team1',1),
('team2',2),
('team3',3)
INSERT INTO #players (
goals,
NAME,
surname,
teamid
)
VALUES
(10,'bob','bob',1),
(2,'bob1','bob',1),
(5,'bob2','bob',1),
(1,'bob3','bob',3),
(3,'bob4','bob',3),
(2,'bob5','bob',3),
(1,'bob6','bob',2),
(2,'bob7','bob',2)
--Create temp table to store team average and teamid
SELECT round(avg(p.Goals), 2) AS average,
t.teamid
INTO #TeamAverages
FROM #players p
LEFT JOIN #teams t
ON p.teamid = t.teamid
GROUP BY t.TeamID
--join on above table and compare to team average table
SELECT p.NAME AS playerName,
p.Surname,
t.NAME AS teamName,
p.Goals,
ta.average
FROM #players p
LEFT JOIN #teams t
ON p.TeamID = t.TeamID
LEFT JOIN #TeamAverages ta
ON ta.teamid = t.teamid
WHERE p.Goals > ta.average
DROP TABLE #players
DROP TABLE #TeamAverages
DROP TABLE #teams