Sqlite查询 - 来自第一列的总和的列

Question

假设我有这个查询

select 
    count(customerid) as Count_Own,
    (select count(customerid) from Customers) Count_ALL 
from 
    Customers
where 
    EmployeeID = 1

它显示了第一列中employeeid = 1和第二列中所有员工的客户数。

现在我想通过代替表Customers来编写类似的查询，我有大的子查询：

select 
    count(customerid) as Count_Own,
    (select count(customerid) from /*BIG QUERY*/) Count_ALL 
from 
    ( /*BIG QUERY*/   )
where 
    EmployeeID = 1

我现在对列Count_ALL有一个问题，因为我想快速计算，而不使用我的子查询。我想知道它是否只是它的解决方案。

Answer 1

解决方法：创建一个假列以加入两个查询：

select 
  count(T1.customerid) as Count_Own, T2.Count_ALL
From ( Select 1 as joinField, --BIG QUERY--   ) T1
join (select count(customerid) Count_ALL, 1 as joinField  
      from customers)  T2
on T1.joinField = T2.joinField
where T1.EmployeeID = 1

编辑到期OP评论。

您可以使用CTE避免两次写大查询。让我们使用这个简化的架构：

dh4@GLOW:~/tmp$ sqlite3 pepe.sql
SQLite version 3.11.0 2016-02-15 17:29:24
Enter ".help" for usage hints.
sqlite> create table t ( i int , e int );
sqlite> insert into t values 
   ...> ( 1,1),
   ...> ( 2,1),
   ...> ( 3,1),
   ...> ( 1,2);

然后，您的查询是：

sqlite> with big_query as
   ...> ( select i,e from t )
   ...> select count(i), (select count(*) from big_query)
   ...> from big_query
   ...> where e=1;
3|4

你也可以使用假连接旅行来避免代理子查询：

sqlite> with big_query as
   ...> ( select i,e from t ),
   ...> q1 as 
   ...> ( select count(*) as n, 1 as fake  from big_query ),
   ...> q2 as
   ...> ( select count(*) as n, 1 as fake from big_query where e=1)
   ...> select q2.n, q1.n
   ...> from q1 inner join q2
   ...> on q1.fake=q2.fake;
3|4

最后一种方法是使用case：

sqlite> select count( case when e = 1 then 1 else null end) , count(*) 
   ...> from t
   ...> ;
3|4