add column unique numbering scheme, more efficient selects

app/Tables/RowNumerator.php

@@ -0,0 +1,32 @@
+<?php
+
+
+namespace App\Tables;
+
+use App\Models\Row;
+
+class RowNumerator
+{
+    /** @var int */
+    private $next;
+    /** @var int */
+    private $last;
+
+    /**
+     * Create a numerator for the given number of rows.
+     *
+     * @param int $capacity
+     */
+    public function __construct($capacity)
+    {
+        list($this->next, $this->last) = Row::allocateRowIDs($capacity);
+    }
+
+    public function next()
+    {
+        if ($this->next > $this->last)
+            throw new \OutOfBoundsException("Row numerator has run out of allocated GRID slots");
+
+        return $this->next++;
+    }
+}