SQL 递归 udf 总是 returns null

Question

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');

上方 "Employees" table 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'、hierarchy/result 应该是 "Victor, Elai"。

谁能指出我在下面的 UDF 中做错了什么。

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;

Answer 1

首先，您不想将其创建为标量函数。它们的性能非常糟糕，您创建的任何 udf 都应该创建为内联 table 值函数。以下内容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

SQL 递归 udf 总是 returns null

SQL recursive udf always returns null

sql

sql-server

recursion

user-defined-functions