How do I use PHP variables as field names in a MySQL query?

Posted on 2009-05-03
Last Modified: 2012-05-06
For example:

{$fieldname = "mygreatfield"}

My current query is:
$query = "SELECT mygreatfield FROM mytable WHERE id=3";

In the query, what is the syntax for replacing "mygreatfield" with the value in $fieldname.

Keep in mind that the $query is already inside <?php  ... ?> tags, so trying to just insert an echo doesn't look right to me, so I didn't even attempt it.

High points on this cause I'm working on a deadline and need an answer fast.
Question by:alicia1234
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LVL 143

Accepted Solution

Guy Hengel [angelIII / a3] earned 500 total points
ID: 24291083
$query = "SELECT {$fieldname} FROM mytable WHERE id=3";
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 24291088
$query = "SELECT `" . $fieldname . "` FROM mytable WHERE id=3";
$query = "SELECT `{$fieldname}` FROM mytable WHERE id=3";

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Author Comment

ID: 24291320
How nice that it's that simple. I should have realized it because I do the same thing for the values. For some reason, I guess I just thought that field names would work differently.

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LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 24291330
glad I could help.
note that you are aware of the difference of the quotes (') for the string values vs the backticks (`) for the table/column names.

Author Comment

ID: 24291347
Should this same syntax work for POST vars? Like this:

$lastfname = "staples"
if ( isset($_POST['{$lastfname}']) ....

because it doesn't see to be working
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 24291357
you put {} where you don't need them

if ( isset($_POST[$lastfname]) ....

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Author Comment

ID: 24291370
Thanks! Again ... ;-)


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