Hi. I hope the title of this post isn't misleading to any of you. I'm trying to collect some data for (a) variable (number of) columns, so I figured I'd first prepare the query (only once) and then pass on the relevant column inside the loop. However, this returns the actual column name, whereas I obviously want the value for this column. I can get it to work and do what I want if I prepare the query inside the loop, but this is exactly what I was trying to avoid. Could anyone explain me why the following doesn't return the value, but the column name?

 
  my $sClassScoresQuery = qq/SELECT ? FROM $exportDb->{pagesTable} WHE
+RE id=?/;
  my $stPageClassScores = $exportDb->{dbh}->prepare($sClassScoresQuery
+);
  my $newClassScore = 0;
  for my $className (keys $hrClassName2Id){
    my $classColumnName = $className . "_score";
    my $classId = $hrClassName2Id->{$className};
    my @aTemp;
    for my $id (@pageTableAutoIncrementIds){
      #prepare here... for debugging purposes only!
      #my $sQuery = qq/SELECT $classColumnName FROM $exportDb->{pagesT
+able} WHERE id = $id/;
      #my $stDebug = $exportDb->{dbh}->prepare($sQuery);
      $stPageClassScores->execute($exportDb->{dbh}->quote_identifier($
+classColumnName), $id);
      #$stDebug->execute();
      while (my @res = $stPageClassScores->fetchrow_array()){
    #while (my @res = $stDebug->fetchrow_array()){
    push @aTemp, $res[0];
      }
    }
  #some other stuff happens here...
}

[download]

So the above code returns the columnname in @res (instead of the value for this column). It works alright if I use the lines currently commented out instead. But this means preparing the statement all the time. I have tried it with a 

bind_param(1, $classColumnName);
bind_param(2, $id)

[download]
, and even bind_param(1, $dbh->quote_identifier($classColumnName)) just before running execute, but that didn't help either. Like I said; could someone maybe explain me what's going on here and why this approach doesn't work? Thanks!

In reply to DBI binding field names as parameters by sinterklaas

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