Question

I got 2 columns in my database that hold text (Products Code and Products Variant).

for example:
Products Code holds the following text: C050101, C070104
and
Products Variant holds the following text: RED, NULL

I want to select all the rows WHERE Code = Products Code AND Variant = Products Variant.
bases on the example I wrote above, I should get 2 rows:
first row WHERE Code=C050101 and Variant=RED
second row WHERE Code=C070104 and Variant IS NULL << IS NULL

I have no idea how to do it…
I would know how to do it if I only need to select only all the rows WHERE Code = Products Code >>

$arr = array('C050101','C070104');
$inclause = implode(',',array_fill(0,count($arr),'?'));
$stockstmt = $pdo->prepare(sprintf("SELECT `id`, `WebTitle`, `StockCode` FROM `stock` WHERE `StockCode` IN(%s)",$inclause));
$stockstmt->execute($arr);

I would really appreciate your help.
Thanks!

Answer 1

You can’t use the IN predicate for this because IN only knows how to compare with = and you need to compare differently to handle the NULLs.

MySQL has a non-standard null-safe equal operator <=> which knows that NULL=NULL is true, and NULL = ‘RED’ is false.

If you use something other than MySQL, your RDBMS might support IS [NOT] DISTINCT which is standard SQL syntax for a similar predicate.

I tested the following and it works:

$arr = array('C050101','RED', 'C070104', NULL);

$sql = "SELECT `id`, `WebTitle`, `StockCode` FROM `stock`
  WHERE (`StockCode`, `StockVariant`) <=> (?, ?)
     OR (`StockCode`, `StockVariant`) <=> (?, ?)";

$stockstmt = $pdo->prepare($sql);
if ($stockstmt === false) { die(print_r($pdo->errorInfo(), true)); }

$status = $stockstmt->execute($arr);
if ($status === false) { die(print_r($stockstmt->errorInfo(), true)); }

I’ll leave it to you how you want to build a list of predicates.

---

Re your comment:

It’s not a recommended practice to use the literal string ‘NULL’ to represent a missing or inapplicable value. That’s what NULL is for in SQL.

If you want a function that makes it more dynamic to build the predicates, try this:

function lookformultiplethings(array $arr)
{
  global $pdo;

  $where = array();
  $values = array();
  foreach ((array) $arr as $term) {
    $where[] = '('
        . join(',', array_map(function ($col) {return "`$col`";}, array_keys($term)))
        . ') <=> ('
        . join(',', array_fill(0,count($term),'?'))
        . ')';
    $values = array_merge($values, array_values($term));
  }
  $sql = "SELECT `id`, `WebTitle`, `StockCode` FROM `stock` ";
  if ($where) {
    $sql .= "WHERE " . join(' OR ', $where);
  }

  $stockstmt = $pdo->prepare($sql);
  if ($stockstmt === false) { die(print_r($pdo->errorInfo(), true)); }

  $status = $stockstmt->execute($values);
  if ($status === false) { die(print_r($stockstmt->errorInfo(), true)); }

  print_r($stockstmt->fetchAll());
}

lookformultiplethings(array(
  array('StockCode' => 'C050101', 'StockVariant' => 'RED'),
  array('StockCode' => 'C070104', 'StockVariant' => 'NULL'),
));

Be careful that the keys of the array you pass are legitimate column names. That is, don’t let user input ever set the column names unless you verify it against a whitelist of real columns.