Question

我正在尝试选择一些数据但是我遇到了问题，因为这是一个子查询，而子查询中的数据是使用连接的别名。我想设置这个是因为我将以不同的方式在子查询上运行聚合。这是一个例子。我希望你明白我在这里要做的事情。这不是我正在使用的实际数据，因此我想使用以下方法。问题是我正在尝试查询具有别名且具有别名的连接的子查询。

请记住，如果我只选择main_query.FullState，如果我有1个连接，则下面有效，但由于我加入了两次，我需要添加一个别名。这是我遇到麻烦的地方。

USERTABLE
----------------

    Name    BirthState     LivingState
    David   CA             CA
    Roger   NY             PA

STATESTABLE
----------------
    State   FullState

    CA      California
    NY      New York
    PA      Philadelphia

select main_query.LivingTable.FullState, count(*) from (
    select * from USERTABLE
    join STATESTABLE LivingTable on USERTABLE.LivingState = STATESTABLE.State
    join STATESTABLE BirthTable on USERTABLE.BirthState = STATESTABLE.State
)main_query

Answer 1

您可以使用已连接表的别名。你甚至无法访问＆＃34;内部＆＃34; table-alias，因为它超出了范围。

如果要检索原始表中具有相同列名的两列，请使用带有AS的列别名。

另一件事：请为这些案件使用WITH。这大大提高了可读性。

WITH main_query AS
(
    select lt.FullState AS LivingFullState, bt.FullState AS BirthFullState
    from USERTABLE ut 
    join STATESTABLE lt on lt.LivingState = ut.State
    join STATESTABLE bt on bt.BirthState = ut.State
)
select LivingFullState, count(*) from main_query

Answer 2

你应该能够运行＆＃34;聚合＆＃34;和其他类型的查询，而不诉诸＆＃34;子查询＆＃34;。只需使用

之类的东西

Select living.FullState as "Living State", count(1)
  from USERTABLE user JOIN STATESTABLE living on living.LivingState = user.State

类似下面的项目可能也很有用

Select State, Sum(LivingStatePopulation) as "Living State Population", Sum(BirthStatePopulation) as "Birth State Population"
  from (Select living.FullState as "State", count(1) as "LivingStatePopulation", 0 as "BirthStatePopulation"
          from USERTABLE user JOIN STATESTABLE living on living.LivingState = user.State 
        UNION
        Select birth.FullState as "State", 0 as "LivingStatePopulation", count(1) as "BirstStatePopulation"
)
order by State

带有连接别名的子查询

2 个答案: