也许将CTE视为用于单个查询的视图的替代品更有意义。但不需要开销、元数据或正式视图的持久性。非常有用，当你需要:

创建递归查询。 在查询中多次使用CTE的结果集。 通过减少大量相同的子查询来提高查询的清晰度。 根据CTE结果集中派生的列启用分组

下面是一个剪切粘贴的例子:

WITH [cte_example] AS (
SELECT 1 AS [myNum], 'a num' as [label]
UNION ALL
SELECT [myNum]+1,[label]
FROM [cte_example]
WHERE [myNum] <=  10
)
SELECT * FROM [cte_example]
UNION
SELECT SUM([myNum]), 'sum_all' FROM [cte_example]
UNION
SELECT SUM([myNum]), 'sum_odd' FROM [cte_example] WHERE [myNum] % 2 = 1
UNION
SELECT SUM([myNum]), 'sum_even' FROM [cte_example] WHERE [myNum] % 2 = 0;

享受

One of the scenarios I found useful to use CTE is when you want to get DISTINCT rows of data based on one or more columns but return all columns in the table. With a standard query you might first have to dump the distinct values into a temp table and then try to join them back to the original table to retrieve the rest of the columns or you might write an extremely complex partition query that can return the results in one run but in most likelihood, it will be unreadable and cause performance issue.

但是通过使用CTE(由Tim Schmelter在选择记录的第一个实例中回答)

WITH CTE AS(
    SELECT myTable.*
    , RN = ROW_NUMBER()OVER(PARTITION BY patientID ORDER BY ID)
    FROM myTable 
)
SELECT * FROM CTE
WHERE RN = 1

如您所见，这更容易阅读和维护。与其他查询相比，它的性能要好得多。

还有一点没有指出，就是速度。我知道这是一个老问题，但我认为这值得直接评论/回答:

它们似乎是多余的，因为派生表也可以这样做

当我第一次使用CTE时，我完全被它的速度惊呆了。这是教科书上的案例，非常适合CTE，但在我使用CTE的所有情况下，都有显著的速度增益。我的第一个查询很复杂，涉及派生表，执行时间很长。对于CTE，它只需要几秒钟，让我震惊，这甚至是可能的。

我认为使用cte有两个原因。

在where子句中使用计算值。对我来说，这似乎比派生表更清晰一些。

假设有两个表-问题和答案由问题连接在一起。ID =答案。Question_Id(和测验id)

WITH CTE AS
(
    Select Question_Text,
           (SELECT Count(*) FROM Answers A WHERE A.Question_ID = Q.ID) AS Number_Of_Answers
    FROM Questions Q
)
SELECT * FROM CTE
WHERE Number_Of_Answers > 0

这是另一个例子，我想要得到一个问题和答案列表。我希望答案与结果中的问题组合在一起。

WITH cte AS
(
    SELECT [Quiz_ID] 
      ,[ID] AS Question_Id
      ,null AS Answer_Id
          ,[Question_Text]
          ,null AS Answer
          ,1 AS Is_Question
    FROM [Questions]

    UNION ALL

    SELECT Q.[Quiz_ID]
      ,[Question_ID]
      ,A.[ID] AS  Answer_Id
      ,Q.Question_Text
          ,[Answer]
          ,0 AS Is_Question
        FROM [Answers] A INNER JOIN [Questions] Q ON Q.Quiz_ID = A.Quiz_ID AND Q.Id = A.Question_Id
)
SELECT 
    Quiz_Id,
    Question_Id,
    Is_Question,
    (CASE WHEN Answer IS NULL THEN Question_Text ELSE Answer END) as Name
FROM cte    
GROUP BY Quiz_Id, Question_Id, Answer_id, Question_Text, Answer, Is_Question 
order by Quiz_Id, Question_Id, Is_Question Desc, Name

 ;with cte as
  (
  Select Department, Max(salary) as MaxSalary
  from test
  group by department
  )  
  select t.* from test t join cte c on c.department=t.department 
  where t.salary=c.MaxSalary;

试试这个

当您希望执行“有序更新”时，它非常有用。

MS SQL不允许你使用ORDER BY UPDATE，但在CTE的帮助下，你可以这样做:

WITH cte AS
(
    SELECT TOP(5000) message_compressed, message, exception_compressed, exception
    FROM logs
    WHERE Id >= 5519694 
    ORDER BY Id
)
UPDATE  cte
SET     message_compressed = COMPRESS(message), exception_compressed = COMPRESS(exception)

看这里更多的信息:如何更新和使用ms sql