[英]How we can use CTE in subquery in sql server?
How we can use a CTE in a subquery in SQL Server?我们如何在 SQL Server 的子查询中使用 CTE?
like:像:
SELECT id (I want to use CTE here), name FROM table_name
Just define your CTE on top and access it in the subquery?只需在顶部定义您的 CTE 并在子查询中访问它?
WITH YourCTE(blubb) AS
(
SELECT 'Blubb'
)
SELECT id,
(SELECT blubb FROM YourCTE),
name
FROM table_name
It doesn't work:它不起作用:
select id (I want to use CTE here), name from table_name
It's not possible to use CTE in sub queries.不能在子查询中使用 CTE。
You can realize it as a work around:您可以将其视为一种解决方法:
CREATE VIEW MyCTEView AS ..here comes your CTE-Statement.
Then you are able to do this:然后你可以这样做:
select id (select id from MyCTEView), name from table_name
Create a view with CTE/ Multiple CTEs with UNION sets of all CTEs使用所有 CTE 的 UNION 集创建具有 CTE/多个 CTE 的视图
CREATE VIEW [dbo].[_vEmployees]
AS
WITH
TEST_CTE(EmployeeID, FirstName, LastName, City, Country)
AS (
SELECT EmployeeID, FirstName, LastName, City, Country FROM Employees WHERE EmployeeID = 4
),
TEST_CTE2
AS (
SELECT EmployeeID, FirstName, LastName, City, Country FROM Employees WHERE EmployeeID = 7
)
SELECT EmployeeID, FirstName, LastName, City, Country FROM TEST_CTE UNION SELECT * FROM TEST_CTE2
GO
Now, use it into sub query现在,将其用于子查询
SELECT * FROM Employees WHERE EmployeeID IN (SELECT EmployeeID FROM _vEmployees)
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