Drupal 7 allows you to pass an array as the second parameter in db_query(). However, in Drupal 6 you need to pass each value in as a separate parameter. Here's how to use call_user_func_array() to call db_query with an unknown number of fields and values

db_query.php

<?php 

//$values is an associative array where the keys are field names and values are the values we want in the database

//create a string with enough %s's for fields and values. Wrap the values in single quotes.
$percents_fields = "";
$percents_values = "";

foreach($values as $field => $value) {
  $percents_fields = "%s, ";
  $percents_values = "'%s', ";
}

//trim off the last comma-space
$percents_fields = rtrim($percents_fields, ", ");
$percents_values = rtrim($percents_values, ", ");

//here's our SQL
$sql = "INSERT INTO table ($percents_fields) VALUES ($percents_values);";

//create an array of parameters we'll send to db_query
$params = array();

//add the SQL
$params[] = $sql;

//add the fields and values
$params = array_merge($params, array_keys($values), $values);

//magic!
call_user_func_array('db_query', $params);

//get the ID of the new row
$new_id = db_last_insert_id('table', 'id');

You could use this method for calling sprintf() as well.

There isn't really a need to call it using the call_user_func_array function is there?

$values = array_merge(array_keys($values), $values);
db_query($sql, $values);

would work just fine according to the code:

<?php
    function db_query($query) {
      $args = func_get_args();
      //take the query out of the args retrieved
      array_shift($args);
      //do the db_prefix magix
      $query = db_prefix_tables($query);
      //if the arg that remains is an array, use it as the args
      if (isset($args[0]) and is_array($args[0])) { // 'All arguments in one array' syntax
          $args = $args[0];
      }
      //... do the rest of the magix
    }

Alternatively you could just use drupal_write_record:

drupal_write_record('table', $values);

Doh. Someone said they tried it with an array, and it didn't work, so I didn't even try it. Thanks for the drupal_write_record() tip.

They probably did it as an array of key value pairs and wondered why it didn't work. Your way is quite innovative though :P

This is why drupal needs a query builder... that way you don't need to worry about building dynamic queries:

if($case_1){
  $query->where('something', $case_1);
}
foreach($input as $k=>$v){
  $query->field($k, $v);
}
$result = $query->insert();

Usually I'm against query builders, but in this case it would have been extremely handy.