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Thread: filtering problem

  1. #1
    Join Date
    Aug 2011
    Location
    Hong Kong
    Posts
    49

    Unhappy filtering problem

    I am making a simple filtering system for visitor that the criteria they choose is either in "column1" or "column2".

    I had a thread regarding to sorting few days ago and I had been told that I can use the clause "IFNULL" and "AS" to solve the problem, but when it comes to filtering it does not work...

    anyway my SQL statement is:

    PHP Code:
    SELECT *, IFNULL(column1,column2) AS finalcolumn FROM mytable WHERE finalcolumn='$visitor_criteria' 

  2. #2
    Join Date
    Jul 2010
    Location
    /ramdisk/
    Posts
    865
    In most SQL flavors, you can not expect an aliased column to behave like a real column. This would drastically change the execution plan of MySQL in an undesirable way. The work-around is to replace the alias with the expression, or to store the expression (per row in a stored procedure) in some variable.

    Try doing it like this:
    PHP Code:
    $resource mysql_query(sprintf(
      
    "SELECT *, 
       IFNULL(column1,column2) AS finalcolumn 
       FROM mytable 
       WHERE IFNULL(column1,column2)='%s'"
    ,
       
    mysql_real_escape_string($visitor_criteria))); 
    edit: I think you might mean to use COALESCE instead of IFNULL

  3. #3
    Join Date
    Aug 2011
    Location
    Hong Kong
    Posts
    49
    thank you for your help eval

    but now i am converting the obsolete mysql to mysqli (which is such a pain to me), so i guess the php code would be like?

    <PHP>
    $resource=$connection->query(sprintf(
    "SELECT *,
    IFNULL(column1,column2) AS finalcolumn
    FROM mytable
    WHERE IFNULL(column1,column2)='%s'",
    mysqli_real_escape_string($link, $visitor_criteria)));
    </PHP>

    ps: i use if "IFNULL" because i want the criteria to be: if column1 is not null then use column1, otherwise use column2, which always contain a value




    also, is there any websites that i can learn mysqli command? i found that php.net is sometimes intimidating
    Last edited by jeffap; 12-17-2012 at 09:08 PM.

  4. #4
    Join Date
    Sep 2011
    Posts
    60
    I think it should be

    <PHP>
    $resource=$connection->query(sprintf(
    "SELECT *,
    IFNULL(column1,column2) AS finalcolumn
    FROM mytable
    WHERE IFNULL(column1,column2) like '%s'",
    mysqli_real_escape_string($link, $visitor_criteria)));
    </PHP>

  5. #5
    Join Date
    Aug 2011
    Location
    Hong Kong
    Posts
    49
    ok i tested the above SQL and it does not work, the error message is as below:

    Fatal error: Fatal error: Call to a member function bind_param() on a non-object in xxx.php on line 132

    i think i would need to use prepared statement...

    i tried to put it like this:

    PHP Code:
    $statement=$connect->prepare("
    SELECT *, 
    IFNULL(column1,column2) AS finalcolumn 
    FROM mytable 
    WHERE finalcolumn=?"
    );

    $statement->bind_param('s',mysqli_real_escape_string($connect,$filtercriteria));

    $statement->execute();

    $statement->bind_result($returned_var1);

    while(
    $statement->fetch()){
        echo 
    $returned_var1 '<br />';

    am i on the right track???


    ps: i followed a tutorial on http://codular.com/php-mysqli

  6. #6
    Join Date
    Aug 2011
    Location
    Hong Kong
    Posts
    49
    almost work out the whole thing...

    PHP Code:
    $statement=$connect->prepare("
    SELECT var1,var2 
    FROM mytable 
    WHERE IFNULL(column1,column2)=?"
    );

    $statement->bind_param('s',mysqli_real_escape_string($connect,$filtercriteria));

    $statement->execute();

    $statement->bind_result($var1$var2); 

    Just asking:
    the SQL command

    PHP Code:
    IFNULL(column1,column2)=? 
    If both column1 and column2 return 'NULL' in some row in my database, will the SQL command still work???

    I have all the above code run without error but the data shows no result and i suspect it has something to do with the IFNULL (or COALESCE that i later use)....
    Last edited by jeffap; 12-21-2012 at 05:29 AM.

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