- Patch #748340 by Berdir, andypost, catch, noahb, Crell: MySQL-optimized tableExists() implementation.

includes/database/mysql/schema.inc

@@ -460,6 +460,40 @@ class DatabaseSchema_mysql extends DatabaseSchema {
     return preg_replace('/; InnoDB free:.*$/', '', $comment);
   }
 
+  public function tableExists($table) {
+    // The information_schema table is very slow to query under MySQL 5.0.
+    // Instead, we try to select from the table in question.  If it fails,
+    // the most likely reason is that it does not exist. That is dramatically
+    // faster than using information_schema.
+    // @link http://bugs.mysql.com/bug.php?id=19588
+    // @todo: This override should be removed once we require a version of MySQL
+    // that has that bug fixed.
+    try {
+      $this->connection->queryRange("SELECT 1 FROM {" . $table . "}", 0, 1);
+      return TRUE;
+    }
+    catch (Exception $e) {
+      return FALSE;
+    }
+  }
+
+  public function fieldExists($table, $column) {
+    // The information_schema table is very slow to query under MySQL 5.0.
+    // Instead, we try to select from the table and field in question. If it
+    // fails, the most likely reason is that it does not exist. That is
+    // dramatically faster than using information_schema.
+    // @link http://bugs.mysql.com/bug.php?id=19588
+    // @todo: This override should be removed once we require a version of MySQL
+    // that has that bug fixed.
+    try {
+      $this->connection->queryRange("SELECT $column FROM {" . $table . "}", 0, 1);
+      return TRUE;
+    }
+    catch (Exception $e) {
+      return FALSE;
+    }
+  }
+
 }
 
 /**