Parameterised queries

I have a query which is created depending on which variables are submitted via a form, an easy example might be:
 
//start the query
$sql= "select tblaccounts.companyid
                ,tblaccounts.accountno
                ,tblmembers.memberno
                ,tblcards.cardno
from tblaccounts
WHERE tblmembers.companyid = '$companyid' ";
 
//build where clauses based on the existence of some variables
if (strlen($firstname)>0){
$sql.= " and tblmembers.firstname = '$firstname' ";}
 
if (strlen($surname)>0){
$sql.= " and tblmembers.surname = '$surname' ";}
 
if (strlen($postcode)>0){
$sql.= " and tblaccounts.postcode = '$postcode' ";            }
 
// complete the query
$sql.= "  and (tblcards.primarycard = 'primary') order by surname, firstname,  postcode";
 
//pass the parameters
$params=array($companyid, $firstname, $surname, $postcode);
 
//run the query
$result=sqlsrv_query($conn, $sql, $params);
 
At the moment I can only run the query using the proper variables, not the ? parameters as the parameter array will change depending on the variables required.

This me open to sql injections and problems with apostrophes etc within variable etc

Is there a way that I can use an associative array to store the possible varaibles and call them within the sql?

I am coding in php 5.6, using mssql on a windows server.
Richard LloydAsked:
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Julian HansenCommented:
Can you not do something like this in your where clause
WHERE 
  (LEN(?) = 0 OR tblmembers.firstname = ?) AND
  (LEN(?) = 0 OR tblmembers.surname = ?) AND
  (LEN(?) = 0 OR and tblaccounts.postcode =?) AND
  (tblcards.primarycard = 'primary')

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In other words lose the 'if' statements and let the query do the checking of the parameter fields - if they are blank then that sub-clause returns TRUE due to the OR otherwise it will check the field against the variable.
EDIT:
The above would obviously require passing the same variable in twice each.

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Richard LloydAuthor Commented:
Thank you, good bit of logic!
Julian HansenCommented:
The other way to do it is

// Array to store parameters for query
$parameters = array();
if (strlen($firstname)>0){
  $sql.= " and tblmembers.firstname = ?";
  $parameters[] = $firstname;
}
 
if (strlen($surname)>0){
  $sql.= " and tblmembers.surname = ? ";
  $parameters[] = $surname
}

if (strlen($postcode)>0){
  $sql.= " and tblaccounts.postcode = ? ";    
  $parameters[] = $postcode;
}
...
// Prepeare statement here  (assuming PDO and $dbh already declared)
$sth = $dbh->prepare($sql);
$sth->execute($parameters);

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Julian HansenCommented:
You are welcome.
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