How to preserve dtype int when reading integers with NaN in pandas

Use dtype 'Int64' for NaN support

• 'Int64' (capital I) is a pandas nullable integer, so it can mix with NaNs.
• Default numpy integers cannot mix with NaNs, so the column will become dtype object.

For example, say column Col D contains only integers and NaNs:

• Either use the dtype param at load time (available in most read_* methods):

  df = pd.read_sql_query(sql_script.read(), engine, dtype={'Col D': 'Int64'})
  #                                                 ^^^^^
  

• Or use astype after loading:

  df = pd.read_sql_query(sql_script.read(), engine).astype({'Col D': 'Int64'})
  #                                                 ^^^^^^