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  1. #1
    Join Date
    Jul 2004

    Unhappy Unanswered: Check if rows are empty or full


    Firstly i have 2 tables for my websms app.

    One table stores just the names of the users groups(like an address book). - wsmsgroups Fields:
    userid - users unique id
    name - name of group(PK because no duplicates)

    The other table store there numbers with name and group for contact. - wsmscontacts

    userid - users unique id
    cgroup - group name
    contact - contacts name
    cellno - cellular number(PK)

    Now my problem:

    I need to get the groups that have contacts. A group might exist if it has no contacts. But I only want the groups that have one or more rows in wsmscontacts table.


  2. #2
    Join Date
    Mar 2004
    name - name of group(PK because no duplicates)
    If more than one user can belong to a group then it isn't a good primary key, use userid instead.

    Also in your second table if a user can share a cell number with someone else it also isn't a good primary key. It is if no one can share a number.

    For your join, use a left outer join and test for not null

    SELECT name FROM wsmsgroups
    ON wmsgroups.userid = wsmscontacts.userid
    AND contact IS NOT NULL

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