avoid throwing the same type of new db exception.

framework/yii/db/Command.php

@@ -278,11 +278,15 @@ class Command extends \yii\base\Component
 			return $n;
 		} catch (\Exception $e) {
 			Yii::endProfile($token, __METHOD__);
+			if ($e instanceof Exception) {
+				throw $e;
+			} else {
 				$message = $e->getMessage() . "\nThe SQL being executed was: $rawSql";
 				$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
 				throw new Exception($message, $errorInfo, (int)$e->getCode(), $e);
 			}
 		}
+	}
 
 	/**
 	 * Executes the SQL statement and returns query result.
@@ -411,11 +415,15 @@ class Command extends \yii\base\Component
 			return $result;
 		} catch (\Exception $e) {
 			Yii::endProfile($token, __METHOD__);
+			if ($e instanceof Exception) {
+				throw $e;
+			} else {
 				$message = $e->getMessage()  . "\nThe SQL being executed was: $rawSql";
 				$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
 				throw new Exception($message, $errorInfo, (int)$e->getCode(), $e);
 			}
 		}
+	}
 
 	/**
 	 * Creates an INSERT command.