message: [external-metadata] Fix unknown column types
diff: @@ -11,6 +11,7 @@ from sqlalchemy import (
  and_, asc, Boolean, Column, DateTime, desc, ForeignKey, Integer, or_,
  select, String, Text,
  )
  +from sqlalchemy.exc import CompileError
  from sqlalchemy.orm import backref, relationship
  from sqlalchemy.schema import UniqueConstraint
  from sqlalchemy.sql import column, literal_column, table, text
  @@ -377,7 +378,10 @@ class SqlaTable(Model, BaseDatasource):
  def external_metadata(self):
  cols = self.database.get_columns(self.table_name, schema=self.schema)
  for col in cols:
  - col['type'] = '{}'.format(col['type'])
  + try:
  + col['type'] = str(col['type'])
  + except CompileError:
  + col['type'] = 'UNKNOWN'
  return cols
  @property
  