SQL server management studio 子查詢

Question

我正在嘗試在 SQL Server management Studio 2016 中運行此子查詢，但它出錯了。 它適用於 MySQL。 請指教：

select count(distinct company) 
from 
(
select company, sum(net_value_gbp) as last2yr_spend 
from Orders 
where bill_date >='01-Jan-2016' 
group by company)
where last2yr_spend >50

Answer 1

別名您的子查詢，如下所示

SELECT COUNT(DISTINCT company)
FROM
(
    SELECT company,
           SUM(net_value_gbp) AS last2yr_spend
    FROM Orders o
    WHERE bill_date >= '01-Jan-2016'
    GROUP BY company
) A
WHERE A.last2yr_spend > 50;

Answer 2

像下面這樣做：

select count(distinct company) 
from 
( select company, sum(net_value_gbp) as last2yr_spend 
from Orders 
where bill_date >= '01-Jan-2016' 
group by company ) 
AS T1
where T1.last2yr_spend > 50

您必須對 sql server 中的子查詢使用ALIAS 。

Answer 3

別名是一個問題。 但是，您應該像這樣編寫查詢：

select count(*) 
from (select company, sum(net_value_gbp) as last2yr_spend 
      from Orders  o
      where bill_date >= '2016-01-01'
      group by company
     ) c
where last2yr_spend > 50;

筆記：

• 請注意子查詢的別名（您的直接問題）。
• 不需要COUNT(DISTINCT) 。 子查詢為每個公司返回一行。 COUNT(DISTINCT)會產生額外的開銷，因此簡單的COUNT(*)就足夠了。
• 日期格式使用 ISO 標准 YYYY-MM-DD。 對於大多數國際化設置，SQL Server 理解這種格式（為了 100% 的完整性，您可以刪除連字符，但我喜歡它們以提高可讀性）。
• 如果company曾經為NULL *並且您不想計算它，則您只需要COUNT(company) （而不是COUNT(*) ）。

Answer 4

select count(company) 
from 
(
select company, sum(net_value_gbp) as last2yr_spend 
from Orders 
where bill_date >='01-Jan-2016' 
group by company
having sum(net_value_gbp) > 50) as T1

Answer 5

子查詢的替代方法是 CTE，我發現它的可讀性稍高一些。 類似於以下內容：

    ;with orders_by_comp as (
          select company, sum(net_value_gbp) as last2yr_spend 
          from Orders  o
          where bill_date >= '2016-01-01'
          group by company)
    select count(distinct company) 
    from orders_by_comp 
    where last2yr_spend > 50;

Answer 6

你可以使用的總和過濾having這樣的：

with cte
AS
(
    select company
    from Orders 
    where bill_date >='01-Jan-2016' 
    group by company
    having sum(net_value_gbp) > 50
) 
select count(distinct company)
from cte;