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Find all rows with no matching rows in second table - MySQL

Hello group, I have two tables: Table A a_id name 1 a 2 b 3 c Table B b_id a_id flag name 1 2 y x 2 2 n y 3 3 n z How can I find the rows from table A where there is no matching row (joined using a_id as key) in table B where flag is "y"? So in this example I want the entries 1/a and 3/c from table A. 2/b should not be selected because there is a row in table B with a_id = 2 and flag="y". Understandable? It seems quite impossible to ...

  1. #1

    Default Find all rows with no matching rows in second table

    Hello group,

    I have two tables:

    Table A
    a_id name
    1 a
    2 b
    3 c

    Table B
    b_id a_id flag name
    1 2 y x
    2 2 n y
    3 3 n z

    How can I find the rows from table A where there is no matching row (joined
    using a_id as key) in table B where flag is "y"?

    So in this example I want the entries 1/a and 3/c from table A. 2/b should
    not be selected because there is a row in table B with a_id = 2 and
    flag="y".

    Understandable?

    It seems quite impossible to me, but I cannot figure out a reason why it is
    impossible, either.

    Regards,
    André


    André Guest

  2. #2

    Default Re: Find all rows with no matching rows in second table


    André Hänsel wrote: 

    Try:
    SELECT A.a_id, A.name
    FROM Table_A A
    LEFT JOIN Table_B B ON A.a_id = B.a_id AND B.flag = "y"
    WHERE B.b_id IS NULL

    Captain Guest

  3. #3

    Default Re: Find all rows with no matching rows in second table

    On Mon, 18 Sep 2006 23:16:42 +0200, André Hänsel wrote: 

    It is time for homework questions already?

    --
    _ o
    |/)
    Peter Guest

  4. #4

    Default Re: Find all rows with no matching rows in second table

    Peter H. Coffin wrote: 
    >
    > It is time for homework questions already?[/ref]

    Hm? What do you want to say? That I haven't made my homework?

    What did I overlook?

    André Guest

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