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SQL count across two tables in a one to many relationship

  • December 8, 2008 at 11:21 pm

    #197062

    I have 2 tables in a one to many relationship, they are subscriber, and SEND_COLLEAGUE_CONTACTS.

    one subscriber has many contacts.

    using the query below i get the userid and the amount of contacts they have.

    SELECT subscribers.userid, Count(SEND_COLLEAGUE_CONTACTS.colleagueID) AS numOfColleagues

    FROM subscribers

    LEFT JOIN SEND_COLLEAGUE_CONTACTS ON SEND_COLLEAGUE_CONTACTS.User_ID = subscribers.userid

    GROUP BY subscribers.userid

    What i want to do is record this number in the subscribers table in a column called ColleagueLimit.

    the query im looking for is basically :

    update subscribers set ColleagueLimit = numOfColleagues where userid is common

    but this is turning out to be more difficult that i thought.

  • December 9, 2008 at 12:22 am

    #909487

    Either of these would do it. My preference is for the second style because it's easier to test.

    UPDATE s SET ColleagueLimit = (SELECT Count(c.colleagueID) AS numOfColleagues

    FROM SEND_COLLEAGUE_CONTACTS c

    WHERE c.[User_ID] = s.userid)

    FROM subscribers s

    UPDATE s SET ColleagueLimit = d.numOfColleagues

    FROM subscribers s

    LEFT JOIN (SELECT [User_ID], Count(c.colleagueID) AS numOfColleagues

    FROM SEND_COLLEAGUE_CONTACTS

    GROUP BY [User_ID]

    ) d ON d.[User_ID] = s.userid

    Cheers

    ChrisM

    “Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw

    For fast, accurate and documented assistance in answering your questions, please read this article.
    Understanding and using APPLY, (I) and (II) Paul White
    Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

  • December 9, 2008 at 12:29 am

    #909488

    Thanks for the quick response and the help.

    😀

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