Sql 合并覆盖

我有一个包含人员及其覆盖期的sql表。很多人都有多个条目，只有在覆盖范围连续的情况下，才应该压缩这些条目。值是varchars，但我可以更改为其他值

Name    effective   termination
John    20160101    20160315
John    20160316    20160501
John    20160601    20161101
John    20160701    20160731
John    20160801    20161231

应该是

John    20160101    20160501
John    20160601    20161231

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这是我的想法。确定每组覆盖范围的起始位置。使用此信息来识别组。然后聚合得到您想要的：

  select name, min(effective) as effective, max(termination) as termination
  from (select t.*,
               sum(case when tprev.name is null then 1 else 0 end) over (partition by name order by effective) as grp
        from t left join
             t tprev
             on t.name = tprev.name and
                t.effective = dateadd(day, 1, tprev.termination)
       ) t
  group by name, grp;