A complex SQL query

 I hope someone can give me some pointers.

 Here is my table.

 +--------+----------+------------+-----------+

 | usr_id | employer | start_date | end_date  |

 +--------+----------+------------+-----------+

 | A      | Goo      | 201904     | -         |

 | A      | Micro    | 201704     | 201903    |

  

 | B      | Micro    | 201706     | -         |

 | B      | Goo      | 201012     | 201705    |

 | B      | Micro    | 201001     | 201011    |

 +--------+----------+------------+-----------+

  

 I am trying to list up people working for a company called "Micro".

 Some people work for a company multiple times, like user B.

 I only need one line per user, displaying only the latest affiliation date.

  

 For user_id "B", I could do Select user_id, MAX(start_date), end_date where employer = 'Micro',

 but that would fail to get record for user_id "A".

  

 If multiple records exist, I want to do MAX, but if only a single record exists, I don't need MAX.

 How do I do that? 

 From the above data, I would like to see only two lines:

 | A      | Micro    | 201704     | 201903    |

 | B      | Micro    | 201706     | -         |

 Thank you.
 
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