用户自定义函数代替游标进行循环拼接

首先,建立测试表,本例我们采用经典的Customer 1-->n Order结构,如下:

USE test
GO

IF EXISTS (SELECT 1 FROM sysobjects WHERE name = 'Orders')
    DROP TABLE Orders
    
IF EXISTS (SELECT 1 FROM sysobjects WHERE name = 'Customers')
    DROP TABLE Customers
    
/*
    Customer 1 --> n Order
*/

-- Create Customer Table
CREATE TABLE Customers
(
    CustomerId UNIQUEIDENTIFIER PRIMARY KEY,
    Name VARCHAR(25),
)
GO


-- Create Order Table
CREATE TABLE Orders
(
    OrderId UNIQUEIDENTIFIER PRIMARY KEY,
    Name VARCHAR(255),
    Customer_Id UNIQUEIDENTIFIER FOREIGN KEY REFERENCES Customers(CustomerId)
)
GO

然后,插入一些测试数据:

-- insert test data for customers table
INSERT INTO Customers
VALUES('65DC24EF-BA13-4707-95B0-3D426C2FD0A0','C1')

INSERT INTO Customers
VALUES('32AA5A01-39B4-42D0-BEE9-9AF64171EB55','C2')
GO


-- insert test data for orders table
INSERT INTO Orders
VALUES('8EAA07D0-0E04-412A-8A60-3178C9C2E205','O1 by C1','65DC24EF-BA13-4707-95B0-3D426C2FD0A0')

INSERT INTO Orders
VALUES('78E0CDAB-A3FA-4317-9D4E-D884F91D41A8','O2 by C2','32AA5A01-39B4-42D0-BEE9-9AF64171EB55')

INSERT INTO Orders
VALUES('D08038A9-94FB-4AFF-9E41-F8BEE0FD4384','O3 by C1','65DC24EF-BA13-4707-95B0-3D426C2FD0A0')

INSERT INTO Orders
VALUES('7487AE08-6313-4DB7-87D7-8F9204F07470','O4 by C2','32AA5A01-39B4-42D0-BEE9-9AF64171EB55')

INSERT INTO Orders
VALUES('49A76769-D074-4AF3-9707-751D34847E2A','O5 by C1','65DC24EF-BA13-4707-95B0-3D426C2FD0A0')

INSERT INTO Orders
VALUES('C5C055EB-49A7-4E4C-82EA-1DB10933C78D','O6 by C2','32AA5A01-39B4-42D0-BEE9-9AF64171EB55')

GO

建立自定义函数:

IF EXISTS (SELECT 1 FROM sysobjects WHERE name = 'fnGetCustomerOrders')
    DROP FUNCTION fnGetCustomerOrders

CREATE FUNCTION fnGetCustomerOrders
(
    @CustomerName VARCHAR(25)
)
    RETURNS VARCHAR(MAX)

AS 

BEGIN
    DECLARE @result VARCHAR(MAX)
    SET @result = ''
    SELECT @result = @result + ', ' + o.Name
    from Customers c INNER JOIN Orders o
            ON c.CustomerId=o.Customer_Id
    WHERE c.Name=@CustomerName
    ORDER by c.Name, o.Name

    IF @result like ', %'
        SET @result = right(@result, len(@result) - 2)

    RETURN @result
END

GO

测试函数:

-- test function
DECLARE @customer_name VARCHAR(25)
SET @customer_name='C1'
SELECT 'Orders By ' + @customer_name + ': ' + dbo.fnGetCustomerOrders(@customer_name)

GO

结果如下:

Orders By C1: O1 by C1, O3 by C1, O5 by C1