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Thread: syntax help please?

  1. #1
    Join Date
    Mar 2006
    Posts
    5

    syntax help please?

    ///CREATE TEMPORARY TABLE distinct_tours
    ///SELECT DISTINCT mtable_bu2.ListID FROM mtable_bu2;
    ///ALTER TABLE virtualdb_bu2 ADD linked tinyint default 0;
    ///UPDATE virtualdb_bu2 i, distinct_tours dt SET i.linked=1
    ///WHERE i.mnum=dt.listID;
    ///DELETE FROM virtualdb_bu2 where linked=0;
    ///ALTER TABLE virtualdb_bu2 DROP COLUMN linked;

    I am trying to delete rows from one table (virtualdb_bu2) that do not have corresponding rows in another table (mtable)

    The join is virtualdb_bu2.mnum = mtable_bu2.ListID.

    I have the above code which seems to break somewhere around UPDATE virtualdb_bu2....

    Any help would be appreciated.

    TIA

  2. #2
    Join Date
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    you can't update 2 tables at once, nor do i understand why you want to try to do that.
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  3. #3
    Join Date
    Mar 2006
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    5
    I didn't think I was....I'm simply trying to delte stuff in one table that is not reffered to another table. I also was muckin about with: ///DELETE FROM virtualdb_bu2 WHERE mnum NOT IN (SELECT ListID FROM mtable_bu2); but that didn't work out either... I'm really kinda frustrated as I must be overthinking this cuase it simply can't be this difficult.

  4. #4
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    this is where you're (trying to) updat(ing) multiple tables
    Code:
    UPDATE virtualdb_bu2 i, distinct_tours dt SET i.linked=1
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  5. #5
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    So instead of: ///UPDATE virtualdb_bu2 i, distinct_tours dt SET i.linked=1

    I should do: UPDATE virtualdb_bu2 i SET i.linked=1

    ??

  6. #6
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    you don't need to (and typically shouldn't) use table aliases in an update, but yes.
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  7. #7
    Join Date
    Mar 2006
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    argh...ok here is what I came up with:
    CREATE TEMPORARY TABLE distinct_tours
    SELECT DISTINCT mtable_bu2.ListID FROM mtable_bu2;
    ALTER TABLE virtualdb_bu2 ADD linked tinyint default 0;
    UPDATE virtualdb_bu2 SET linked=1
    WHERE virtualdb_bu2.mlsnum=mtable_bu2.ListID;
    DELETE FROM virtualdb_bu2 where linked=0;
    ALTER TABLE virtualdb_bu2 DROP COLUMN linked;

    of course it dosn't work either but..... it LOOKS good!

    MySQL said:


    #1109 - Unknown table 'mtable_bu2' in where clause
    Last edited by design@glyndowe; 03-26-2006 at 07:09 PM.

  8. #8
    Join Date
    Mar 2006
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    DELETE FROM c USING virtualdb_bu2 c LEFT JOIN mtable_bu2 w ON c.mlsnum = w.ListID WHERE w.ListID IS NULL

    also did not work...syntax error...

  9. #9
    Join Date
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    Quote Originally Posted by design@glyndowe
    I am trying to delete rows from one table (virtualdb_bu2) that do not have corresponding rows in another table (mtable)
    If that's what you want to do, then why are you using CREATE and ALTER. Those are used to create a new table and to alter the structure of a table respectively.

    Do you have to do it in one SQL instruction?
    I'm not sure what language you are using, but something like this could work for you
    Code:
    PSEUDO CODE:
    
    SELECT DISTINCT mlsnum FROM virtualdb_bu2
    (use DISTINCT here so you only get one of each occurance.
     Otherwise it will try to delect non-existant items that will cause an error) 
    while (fetch loop) {
      found = ...SELECT COUNT(*) FROM mtable_bu2 WHERE ListID=<fetched item>
      if (!found) {
        DELETE FROM virtualdb_bu2 WHERE mlsnum = <fetched item>
      }
    }

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