--- includes/Block.php~	2005-02-03 22:07:20.000000000 +0100
+++ includes/Block.php	2005-02-03 22:07:20.000000000 +0100
@@ -81,10 +81,17 @@
 			$sql = "SELECT * FROM $ipblocks WHERE ipb_user={$user} $options";
 		} elseif ($user=="") {
 			$sql = "SELECT * FROM $ipblocks WHERE ipb_address='" . $db->strencode( $address ) . "' $options";
-		} else {
-			$sql = "SELECT * FROM $ipblocks WHERE (ipb_address='" . $db->strencode( $address ) . 
-				"' OR ipb_user={$user}) $options";
-		}
+                } elseif ( $options=='' ) {
+                        # If there are no options (e.g. FOR UPDATE), use a UNION
+                        # so that the query can make efficient use of indices
+                        $sql = "SELECT * FROM $ipblocks WHERE ipb_address='" . $db->strencode( $address ) .
+                                "' UNION SELECT * FROM $ipblocks WHERE ipb_user={$user}";
+                } else {
+                        # If there are options, a UNION can not be used, use one
+                        # SELECT instead. Will do a full table scan.
+                        $sql = "SELECT * FROM $ipblocks WHERE (ipb_address='" . $db->strencode( $address ) . 
+                                "' OR ipb_user={$user}) $options";
+                }
 
 		$res = $db->query( $sql, $fname );
 		if ( 0 == $db->numRows( $res ) ) {