联合表以从所有表中获取唯一记录集的正确方法是什么？

Question

我有以下示例：

而且我不知道如何在这些表之间进行适当的合并

Answer 1

列是否不同？如果是这样，只需将它们填充为空：

select a, b, c, null as d from t1 union all
select a, b, c, null as d from t2 union all
select a, b, c, null as d from t3 union all
select a, b, c, null as d from t4 union all
select a, null as b, null as c, d from t5 union all
select a, null as b, null as c, d from t6 union all
select a, null as b, null as c, d from t7