[FEAT MERGE] Support external table

Co-authored-by: jingtaoye35 <1255153887@qq.com>

unittest/sql/parser/test_parser.result

@@ -5653,7 +5653,8 @@ question_mask_size: 0
               ]
             }
           ]
-        }
+        },
+         { }
       ]
     }
   ]
@@ -5748,7 +5749,8 @@ question_mask_size: 0
               ]
             }
           ]
-        }
+        },
+         { }
       ]
     }
   ]
@@ -5848,7 +5850,8 @@ question_mask_size: 0
               ]
             }
           ]
-        }
+        },
+         { }
       ]
     }
   ]