SQL递归udf总是返回null

Posted 2023-04-13

【中文标题】SQL递归udf总是返回null

【英文标题】：SQL recursive udf always returns null

【发布时间】：2017-09-28 03:22:30

【问题描述】：

Create Table Employees
(
    Employee varchar(10),
    Manager varchar(10)
);

Insert into Employees
values
('Charlie',null),
('Peter','James'),
('Elai',null),
('Graham','Emanuel'),
('Amanda','Charlie'),
('Sen','Graham'),
('Emanuel',null),
('James','Amanda'),
('Elai',null),
('Victor','Elai');

“员工”表上方包含员工和员工的经理姓名。尝试使用以下函数检索员工的逗号分隔层次结构时，结果始终为空。

例如： 员工'Victor'，层次结构/结果应为"Victor, Elai"。

谁能指出我在 UDF 下面做错了什么。

Create Function EmployeeHierarchy(@employeeName varchar(20))
Returns varchar(100)
AS 
Begin
    Declare @commaSeparatedHierarchy varchar(100);
    Declare @manager varchar(20);

    if(@employeeName is not null)
    Begin       
        Select @manager=Manager from Employees where Employee=@employeeName;
        Set @commaSeparatedHierarchy=dbo.EmployeeHierarchy(@manager)+','+@manager;      
    End

    return @commaSeparatedHierarchy;
End;

【问题讨论】：

测试数据加1

【参考方案1】：

首先，您不想将其创建为标量函数。它们的性能是可怕的任何你创建的 udf，应该被创建为一个内联表值函数。以下应该可以满足您的需求...

-- the test data...
USE tempdb;
GO 
IF OBJECT_ID('tempdb.dbo.Employee', 'U') IS NOT NULL 
DROP TABLE dbo.Employee;

CREATE TABLE dbo.Employee ( 
    Employee varchar(10),
    Manager varchar(10)
    );
INSERT dbo.Employee (Employee, Manager) VALUES
    ('Charlie',null),
    ('Peter','James'),
    ('Elai',null),
    ('Graham','Emanuel'),
    ('Amanda','Charlie'),
    ('Sen','Graham'),
    ('Emanuel',null),
    ('James','Amanda'),
    ('Elai',null),
    ('Victor','Elai');

SELECT * FROM dbo.Employee e;

iTVF 代码...

CREATE FUNCTION dbo.EmployeeHierarchy
(
    @employeeName varchar(20)
)
RETURNS TABLE WITH SCHEMABINDING AS
RETURN
    WITH
        cte_Recur AS (
            SELECT 
                CSH = CAST(CONCAT(e.Employee, ', ' + e.Manager) AS VARCHAR(1000)),
                e.Manager,
                NodeLevel = 1
            FROM
                dbo.Employee e
            WHERE 
                e.Employee = @employeeName
            UNION ALL 
            SELECT 
                CSH = CAST(CONCAT(r.CSH, ', ' + e.Manager) AS VARCHAR(1000)),
                e.Manager,
                NodeLevel = r.NodeLevel + 1
            FROM
                dbo.Employee e
                JOIN cte_Recur r
                    ON e.Employee = r.Manager
            WHERE 
                e.Manager IS NOT NULL
            )
    SELECT
        commaSeparatedHierarchy = MAX(r.CSH)
    FROM
        cte_Recur r;
GO 

示例执行...

SELECT 
    eh.commaSeparatedHierarchy
FROM
    dbo.EmployeeHierarchy('peter') eh;

...结果...

commaSeparatedHierarchy
------------------------------
Peter, James, Amanda, Charlie

【讨论】：

谢谢你，杰森。