DBI always auto quotes placeholders. Which can be annoying if you want to use a placeholder to represent what you are selecting and not what you are comparing.

## You can do this, and not worry about quoting:
$query = "SELECT x, y, z from table where a = ?";
## This doesn't work the way you think it does:
$query = "SELECT ? from table where a = 'blah'";
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In the case of the second example above, if you provided "field1" to be bound to the placeholder, you would get: SELECT "field1" from table where a = 'blah', which means you would get a bunch of results that all say "field1".