Placeholders are used to plug data into SQL statements. They cannot be used to alter the statements themselves. What you asked the database to do was this:

If you need to query different fields at different times, each will need it's own query statement. The alternative would be to ask for all fields and only read out the one you wanted from the response.

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print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';
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