Question

I’m writing a program for a running contest using SQLite database, and I have to determine teams from the finish data. There are schools taking part of the contest, and one team consist of four(exactly four) people from one school. A school can have more than one team. The team position is determined by the sum of the members positions. The contestants are stored in one table with their finish position name and school.

Can it be done by SQL query or should I solve it in code?

Example:
pos     name    school            pos    name     school
1      person1   foo               1     person1   foo
2      person2   foo               2     person2   foo
3      person3   bar               6     person6   foo
4      person4   bar               8     person8   foo
5      person5   bar     ->        3     person3   bar
6      person6   foo               4     person4   bar
7      person7   bar               5     person5   bar
8      person8   foo               7     person7   bar
9      person9   foo
10     person10  foo
11     person11  bar

Answer 1

I know there is nothing like ROW_NUMBER() OVER… in SQLite, but I cannot find anything about something similar to a CROSS APPLY.

If there is something equivalent to a CROSS APPLY, then you can do the following. (EDIT: I noticed the requirement for schools to be able to have multiple teams. This solution would only work with one team per school. You will need a recursive CTE and ROW_NUMBER as far as I can tell, otherwise—which are not available in SQLite to my knowledge)

SELECT  TeamTable.*
FROM    Table
CROSS APPLY
    (
        SELECT  TOP 4 *
        FROM Table AS InnerTable
        WHERE   InnerTable.school = Table.School
        ORDER BY InnerTable.Pos
    ) AS TeamTable

If not, then you would probably have to use a while loop and temp tables to fill this. If that is the case, then there is no real gain from using the SQL and I would suggest going the code route.

EDIT:
However, this is the temp table solution as was requested. You need the inner while since you could have multiple teams within the school (something I had disregarded before and makes the CROSS APPLY solution not work without a recursive CTE and ROW_NUMBER, which has been edited to acknowledge)

CREATE TABLE #SchoolList 
    (Id INT IDENTITY(1,1), School VARCHAR(50))

INSERT INTO #SchoolList
SELECT DISTINCT School
FROM TeamTable

CREATE TABLE #TeamList
    (TeamNumber INT IDENTITY(1,1), Pos INT, Name VARCHAR(50),
        School VARCHAR(50))

DECLARE @CurrentSchool VARCHAR(50), @CurrentSchoolPos INT
DECLARE @CurrentSchoolLookupId INT
SET @CurrentSchoolId = 1
WHILE EXISTS (SELECT 1 FROM #SchoolList WHERE Id > @CurrentSchoolLookupId)
BEGIN
    SELECT @CurrentSchool = School FROM #SchoolList
        WHERE Id = @CurrentSchoolLookupId
    SET @CurrentSchoolPos = SELECT TOP 1 Pos FROM TeamTable 
                            WHERE School = @CurrentSchool 
                            ORDER BY POS
    WHILE ISNULL(@CurrentSchoolPos, 0) > 0
    BEGIN
        INSERT INTO #TeamList
        SELECT Pos, Name, School 
        FROM TeamTable 
        WHERE School = @CurrentSchool AND Pos = @CurrentSchoolPos

        SET @CurrentSchoolPos = SELECT TOP 1 Pos FROM TeamTable 
                                WHERE School = @CurrentSchool 
                                    AND Pos > @CurrentSchoolPos ORDER BY POS
    END
    SET @CurrentSchoolLookupId = @CurrentSchoolLookupId + 1
END

SELECT * FROM #TeamList