MySQL-如何从组合表中所有列的一列中提取数据

Question

我想从组合表中所有列的一列中提取数据。它适用于 SELECT 方法。

ID   FirstName   LastName
1      John        Doe
2      Bugs        Bunny
3      Kim        Johnson

我该如何将结果显示为:

ALIAS
1
2
3
John
Bugs
Kim
Doe
Bunny
Johnson

谢谢你帮助我

Answer 1

您需要 UNION(或 UNION ALL)查询:

select ID as ALIAS from tablename
union all
select FirstName as ALIAS from tablename
union all
select LastName as ALIAS from tablename

UNION 查询将返回不同的值，UNION ALL 则返回所有值。如果你想保留顺序，则需要额外的一列:

select ALIAS from
(
  select id, ID as ALIAS, 1 as col from tablename
  union all
  select id, FirstName, 2 as col from tablename
  union all
  select id, LastName, 3 as col from tablename
) s
order by col, id