diff -urN drupal-7.x-dev/includes/database/mysql/query.inc drupal-7.x-dev-comments/includes/database/mysql/query.inc
--- drupal-7.x-dev/includes/database/mysql/query.inc	2010-04-19 14:43:05.000000000 +1000
+++ drupal-7.x-dev-comments/includes/database/mysql/query.inc	2010-05-07 13:40:23.752229806 +1000
@@ -43,6 +43,8 @@
   }
 
   public function __toString() {
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
 
     // Default fields are always placed first for consistency.
     $insert_fields = array_merge($this->defaultFields, $this->insertFields);
@@ -50,10 +52,10 @@
     // If we're selecting from a SelectQuery, finish building the query and
     // pass it back, as any remaining options are irrelevant.
     if (!empty($this->fromQuery)) {
-      return "INSERT INTO {" . $this->table . '} (' . implode(', ', $insert_fields) . ') ' . $this->fromQuery;
+      return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') ' . $this->fromQuery;
     }
 
-    $query = "INSERT INTO {" . $this->table . '} (' . implode(', ', $insert_fields) . ') VALUES ';
+    $query = $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') VALUES ';
 
     $max_placeholder = 0;
     $values = array();
@@ -143,6 +145,8 @@
 
 
   public function __toString() {
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
 
     // Set defaults.
     if ($this->updateFields) {
@@ -164,7 +168,7 @@
 
     $insert_fields = $this->insertFields + $this->keyFields;
 
-    $query = "INSERT INTO {" . $this->table . '} (' . implode(', ', array_keys($insert_fields)) . ') VALUES ';
+    $query = $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', array_keys($insert_fields)) . ') VALUES ';
 
     $max_placeholder = 0;
     $values = array();
diff -urN drupal-7.x-dev/includes/database/pgsql/query.inc drupal-7.x-dev-comments/includes/database/pgsql/query.inc
--- drupal-7.x-dev/includes/database/pgsql/query.inc	2009-09-11 12:47:11.000000000 +1000
+++ drupal-7.x-dev-comments/includes/database/pgsql/query.inc	2010-05-07 13:40:23.793479900 +1000
@@ -71,6 +71,8 @@
   }
 
   public function __toString() {
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
 
     // Default fields are always placed first for consistency.
     $insert_fields = array_merge($this->defaultFields, $this->insertFields);
@@ -78,10 +80,10 @@
     // If we're selecting from a SelectQuery, finish building the query and
     // pass it back, as any remaining options are irrelevant.
     if (!empty($this->fromQuery)) {
-      return "INSERT INTO {" . $this->table . '} (' . implode(', ', $insert_fields) . ') ' . $this->fromQuery;
+      return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') ' . $this->fromQuery;
     }
 
-    $query = "INSERT INTO {" . $this->table . '} (' . implode(', ', $insert_fields) . ') VALUES ';
+    $query = $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') VALUES ';
 
     $max_placeholder = 0;
     $values = array();
diff -urN drupal-7.x-dev/includes/database/query.inc drupal-7.x-dev-comments/includes/database/query.inc
--- drupal-7.x-dev/includes/database/query.inc	2010-04-19 14:43:05.000000000 +1000
+++ drupal-7.x-dev-comments/includes/database/query.inc	2010-05-07 13:49:58.103770099 +1000
@@ -239,6 +239,11 @@
    */
   protected $nextPlaceholder = 0;
 
+  /**
+   * An array of comments that can be prepended to a query.
+   */
+  protected $comments = array();
+
   public function __construct(DatabaseConnection $connection, $options) {
     $this->connection = $connection;
     $this->queryOptions = $options;
@@ -262,6 +267,38 @@
   public function nextPlaceholder() {
     return $this->nextPlaceholder++;
   }
+
+  /*
+   * Adds a comment to the comments array for the query. Needs to return
+   * the query object to make the call chainable.
+   *
+   * @return
+   *   The query object.
+   */
+  public function addComment($comment) {
+    $this->comments[] = $comment;
+    return $this;
+  }
+
+  /**
+   * Returns a reference to the comments array for the query.
+   *
+   * Because this method returns by reference, alter hooks may edit the fields
+   * array directly to make their changes. If just adding fields, however, the
+   * use of addComment() is preferred.
+   *
+   * Note that this method must be called by reference as well:
+   *
+   * @code
+   * $comments =& $query->getComments();
+   * @endcode
+   *
+   * @return
+   *   A reference to the fields array structure.
+   */
+  public function &getComments() {
+    return $this->comments;
+  }
 }
 
 /**
@@ -467,11 +504,14 @@
 
   public function __toString() {
 
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
+
     // Default fields are always placed first for consistency.
     $insert_fields = array_merge($this->defaultFields, $this->insertFields);
 
     if (!empty($this->fromQuery)) {
-      return "INSERT INTO {" . $this->table . '} (' . implode(', ', $insert_fields) . ') ' . $this->fromQuery;
+      return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') ' . $this->fromQuery;
     }
 
     // For simplicity, we will use the $placeholders array to inject
@@ -481,7 +521,7 @@
     $placeholders = array_pad($placeholders, count($this->defaultFields), 'default');
     $placeholders = array_pad($placeholders, count($this->insertFields), '?');
 
-    return 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') VALUES (' . implode(', ', $placeholders) . ')';
+    return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') VALUES (' . implode(', ', $placeholders) . ')';
   }
 
   /**
@@ -899,7 +939,11 @@
   }
 
   public function __toString() {
-    $query = 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '} ';
+
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
+
+    $query = $comments . 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '} ';
 
     if (count($this->condition)) {
 
@@ -939,7 +983,10 @@
   }
 
   public function __toString() {
-    return 'TRUNCATE {' . $this->connection->escapeTable($this->table) . '} ';
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
+
+    return $comments . 'TRUNCATE {' . $this->connection->escapeTable($this->table) . '} ';
   }
 }
 
@@ -1099,6 +1146,10 @@
   }
 
   public function __toString() {
+
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
+
     // Expressions take priority over literal fields, so we process those first
     // and remove any literal fields that conflict.
     $fields = $this->fields;
@@ -1113,7 +1164,7 @@
       $update_fields[] = $field . '=:db_update_placeholder_' . ($max_placeholder++);
     }
 
-    $query = 'UPDATE {' . $this->connection->escapeTable($this->table) . '} SET ' . implode(', ', $update_fields);
+    $query = $comments . 'UPDATE {' . $this->connection->escapeTable($this->table) . '} SET ' . implode(', ', $update_fields);
 
     if (count($this->condition)) {
       $this->condition->compile($this->connection, $this);
diff -urN drupal-7.x-dev/includes/database/select.inc drupal-7.x-dev-comments/includes/database/select.inc
--- drupal-7.x-dev/includes/database/select.inc	2010-04-28 22:36:26.000000000 +1000
+++ drupal-7.x-dev-comments/includes/database/select.inc	2010-05-07 13:40:23.793479900 +1000
@@ -1286,8 +1286,11 @@
 
   public function __toString() {
 
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
+
     // SELECT
-    $query = 'SELECT ';
+    $query = $comments . 'SELECT ';
     if ($this->distinct) {
       $query .= 'DISTINCT ';
     }
Binary files drupal-7.x-dev/includes/database/.select.inc.swp and drupal-7.x-dev-comments/includes/database/.select.inc.swp differ
diff -urN drupal-7.x-dev/includes/database/sqlite/query.inc drupal-7.x-dev-comments/includes/database/sqlite/query.inc
--- drupal-7.x-dev/includes/database/sqlite/query.inc	2009-11-02 11:19:27.000000000 +1100
+++ drupal-7.x-dev-comments/includes/database/sqlite/query.inc	2010-05-07 13:40:23.793479900 +1000
@@ -33,16 +33,19 @@
   }
 
   public function __toString() {
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
+
     // Produce as many generic placeholders as necessary.
     $placeholders = array_fill(0, count($this->insertFields), '?');
 
     // If we're selecting from a SelectQuery, finish building the query and
     // pass it back, as any remaining options are irrelevant.
     if (!empty($this->fromQuery)) {
-      return "INSERT INTO {" . $this->table . '} (' . implode(', ', $this->insertFields) . ') ' . $this->fromQuery;
+      return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $this->insertFields) . ') ' . $this->fromQuery;
     }
 
-    return 'INSERT INTO {' . $this->table . '} (' . implode(', ', $this->insertFields) . ') VALUES (' . implode(', ', $placeholders) . ')';
+    return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $this->insertFields) . ') VALUES (' . implode(', ', $placeholders) . ')';
   }
 
 }
@@ -143,7 +146,10 @@
  */
 class TruncateQuery_sqlite extends TruncateQuery {
   public function __toString() {
-    return 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '} ';
+    // Create a comments string to prepend to the query.
+    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';
+
+    return $comments . 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '} ';
   }
 }