SQL查詢獲得計數分組的項目

Question

我有下面的表：

agent  status 

A   Mail Sent 
B   Fax Sent 
A   Fax Sent 
B   Mail Sent 
B   Mail Sent 
B   Fax Sent 

我想要得到這樣的結果：

Agent Fax_Count Mail_Count 

A  1   1 
B  2   2 

Answer 1

你可以嘗試這樣的事情

DECLARE @TABLE TABLE(
    agent VARCHAR(10), 
    status VARCHAR(10) 
) 

INSERT INTO @TABLE (agent,status) SELECT 'A','Mail Sent' 
INSERT INTO @TABLE (agent,status) SELECT 'B','Fax Sent' 
INSERT INTO @TABLE (agent,status) SELECT 'A','Fax Sent' 
INSERT INTO @TABLE (agent,status) SELECT 'B','Mail Sent' 
INSERT INTO @TABLE (agent,status) SELECT 'B','Mail Sent' 
INSERT INTO @TABLE (agent,status) SELECT 'B','Fax Sent' 

SELECT agent, 
     SUM(CASE WHEN status = 'Mail Sent' THEN 1 ELSE 0 END) Mail_Count , 
     SUM(CASE WHEN status = 'Fax Sent' THEN 1 ELSE 0 END) Fax_Count 
FROM @TABLE 
GROUP BY agent 

Answer 2

select Name, SUM(MailSent),SUM(FaxSent) 
    from 
    (
    select 
    case Status when 'Mail Sent' then 1 else 0 end as MailSent , 
    case Status when 'Fax Sent' then 1 else 0 end as FaxSent , 
    Name 
    from Agents 
) tmp 

Answer 3

作爲旁觀者的替代選擇（好）解決方案：

SELECT agent, 
     (SELECT COUNT(*) FROM myTable WHERE agent = t.agent AND status = 'Mail Sent') Mail_Count, 
     (SELECT COUNT(*) FROM myTable WHERE agent = t.agent AND status = 'Fax Sent') Fax_Count 
FROM myTable t 
GROUP BY agent 

根據數據的分佈情況，如果查詢分析工具發現的性能可能會比他的解決方案（在計算字段沒有SUM）或更糟（子選擇）或等於（更好兩種情況下的最佳執行計劃）。

Answer 4

你可以這樣做......可能不是最優雅的，但它的工作... 剛換出@Table與你查詢的表...

SELECT DISTINCT 
    T.AGENT, 
    (SELECT COUNT(AGENT) FROM @TABLE WHERE AGENT = T.AGENT AND Status LIKE 'Fax%') AS Fax_Count, 
    (SELECT COUNT(AGENT) FROM @TABLE WHERE AGENT = T.AGENT AND Status LIKE 'Mail%') AS Email_Count 
FROM 
    @TABLE T 

Answer 5

這是新的方式（因爲SQL Server 2005中），以解決用PIVOT功能問題：

SELECT agent, [Mail Sent] AS Mail_Count, [Fax Sent] AS Fax_Count 
FROM 
(
    SELECT T.agent, T.status, COUNT(*) AS Counter 
    FROM tblAgents AS T 
    GROUP BY T.agent, T.status 
) AS Data 
PIVOT 
(
    SUM(Counter) FOR [status] IN ([Mail Sent], [Fax Sent]) 
) AS PivotTable 

我不使用這個我自己很多時候由於更復雜的語法，但也許有一些性能來獲取？