smarthall smarthall - 7 months ago 13
SQL Question

MySQL Prepared statements with a variable size variable list

How would you write a prepared MySQL statement in PHP that takes a differing number of arguments each time? An example such query is:

SELECT `age`, `name` FROM `people` WHERE id IN (12, 45, 65, 33)


The
IN
clause will have a different number of
id
s each time it is run.

I have two possible solutions in my mind but want to see if there is a better way.

Possible Solution 1 Make the statement accept 100 variables and fill the rest with dummy values guaranteed not to be in the table; make multiple calls for more than 100 values.

Possible Solution 2 Don't use a prepared statement; build and run the query checking stringently for possible injection attacks.

Answer

I can think of a couple solutions.

One solution might be to create a temporary table. Do an insert into the table for each parameter that you would have in the in clause. Then do a simple join against your temporary table.

Another method might be to do something like this.

$dbh=new PDO($dbConnect, $dbUser, $dbPass);
$parms=array(12, 45, 65, 33);
$parmcount=count($parms);   // = 4
$inclause=implode(',',array_fill(0,$parmcount,'?')); // = ?,?,?,?
$sql='SELECT age, name FROM people WHERE id IN (%s)';
$preparesql=sprintf($sql,$inclause);  // = example statement used in the question
$st=$dbh->prepare($preparesql);
$st->execute($parms);

I suspect, but have no proof, that the first solution might be better for larger lists, and the later would work for smaller lists.


To make @orrd happy here is a terse version.

$dbh=new PDO($dbConnect, $dbUser, $dbPass);
$parms=array(12, 45, 65, 33);
$st=$dbh->prepare(sprintf('SELECT age, name FROM people WHERE id IN (%s)',
                          implode(',',array_fill(0,count($parms),'?')));
$st->execute($parms);