Question

I have a problem incorporating a Group_Concat function in my SQL query. I have tried to work around it with PHP, but I would prefer to get it right with SQL instead. My code is below, I am using the latest version of MYSQL.

SELECT Main.Title, Main.DatePrint, Main.PerformanceDate, Main.Unsure_Sure, Main.Register, Main.notes, 
VenueKey.Venue,AuthorKey.Author, CompanyKey.Company, PrintKey.Printer, SourceKey.Source 
FROM Main INNER JOIN MainVenue
    ON Main.MainID = MainVenue.ID_V
    INNER JOIN VenueKey
    ON MainVenue.VenueID = VenueKey.ID_V_K

    INNER JOIN MainAuthor
    ON Main.MainID = MainAuthor.ID_A
    INNER JOIN AuthorKey
    ON MainAuthor.AuthorID = AuthorKey.ID_A_K

    INNER JOIN MainCompany
    ON Main.MainID = MainCompany.ID_C
    INNER JOIN CompanyKey
    ON MainCompany.CompanyID = CompanyKey.ID_C_K

    INNER JOIN MainPrinter
    ON Main.MainID = MainPrinter.ID_P
    INNER JOIN PrintKey
    ON MainPrinter.PrinterID = PrintKey.ID_P_K

    INNER JOIN MainSource
    ON Main.MainID = MainSource.ID_S
    INNER JOIN SourceKey
    ON MainSource.SourceID = SourceKey.ID_S_K

Ideally I would like to use a Group_Concat on Author, Venue, and Company but I have been having a hard time getting it to work, with it instead returning a null value. Please let me know what if there is anything I can do to fix this.

Thanks.

Answer 1

You must be grouping the results in order for GROUP_CONCAT to have something to work with. Try something along the lines of:

SELECT
  AuthorKey.Author,
  GROUP_CONCAT(VenueKey.Venue) AS all_venues,
  GROUP_CONCAT(CompanyKey.Company) AS all_companies
...
GROUP BY AuthorKey.Author

to get a list of the authors with a concatenated list of venues and companies for example.