sql-server - 如何在sql server中调用递归函数

Question

我有一个表格如下

cat_id  Cat_Name    Main_Cat_Id

1       veg         null
2       main course 1
3       starter     1
4       Indian      2
5       mexican     2
6       tahi        3
7       chinese     3
8       nonveg      null
9       main course 8
10      indian      9
11      starter     8
12      tahi        11
13      chinese     11

(Main_Cat_Id 是之前添加的所属类别的 cat_id)

此表用于产品类别，其中蔬菜类别有两个子类别主菜和开胃菜，由<标识强>main_cat_id这些子类别再次有子类别为印度和墨西哥

这种分类取决于用户；他还可以向印度、墨西哥添加更多子类别，这样他就可以有任何级别的分类

现在我必须选择任何节点的所有子类别，就像如果我选择蔬菜我必须选择

(1)veg > (2)main course(1) > (4)indian(2)
                           > (5)mexican(2)
       > (3)starter(1)     > (6)thai(3)
                           > (7)chinese(3)

将字符串组成为 1,2,4,5,3,6,7

为此，我编写了一个 sql 函数

CREATE FUNCTION [dbo].[GetSubCategory_TEST]
( @MainCategory int, @Category varchar(max))
RETURNS varchar(max)
AS
BEGIN
    IF EXISTS (SELECT Cat_Id FROM Category WHERE Main_Cat_Id=@MainCategory)
    BEGIN
        DECLARE @TEMP TABLE
        (
            CAT_ID INT
        )
        INSERT INTO @TEMP(CAT_ID) SELECT Cat_Id FROM Category WHERE Main_Cat_Id=@MainCategory
        DECLARE @TEMP_CAT_ID INT
        DECLARE CUR_CAT_ID CURSOR FOR SELECT CAT_ID FROM @TEMP
            OPEN CUR_CAT_ID
            WHILE 1 =1
                BEGIN
                FETCH NEXT FROM CUR_CAT_ID
                INTO  @TEMP_CAT_ID;
                IF @@FETCH_STATUS <> 0
                    SET @Category=@Category+','+ CONVERT(VARCHAR(50), @TEMP_CAT_ID)
                    SET @Category = [dbo].[GetSubCategory](@TEMP_CAT_ID,@Category)
                END
                CLOSE CUR_CAT_ID
                DEALLOCATE CUR_CAT_ID
    END
    return @Category
END 

但是这个函数继续执行并且没有给出所需的输出我不明白发生了什么问题请帮助我得到这个

Answer 1

您不需要递归函数来构建它，您可以使用递归 CTE为此。

类似于

DECLARE @TABLE TABLE(
    cat_id INT,
    Cat_Name VARCHAR(50),
    Main_Cat_Id INT
)

INSERT INTO @TABLE SELECT 1,'veg',null
INSERT INTO @TABLE SELECT 2,'main course',1
INSERT INTO @TABLE SELECT 3,'starter',1
INSERT INTO @TABLE SELECT 4,'Indian',2
INSERT INTO @TABLE SELECT 5,'mexican',2
INSERT INTO @TABLE SELECT 6,'tahi',3
INSERT INTO @TABLE SELECT 7,'chinese',3
INSERT INTO @TABLE SELECT 8,'nonveg',null
INSERT INTO @TABLE SELECT 9,'main course',8
INSERT INTO @TABLE SELECT 10,'indian',9
INSERT INTO @TABLE SELECT 11,'starter',8
INSERT INTO @TABLE SELECT 12,'tahi',11
INSERT INTO @TABLE SELECT 13,'chinese',11

;WITH Recursives AS (
        SELECT  *,
                CAST(cat_id AS VARCHAR(MAX)) + '\' ID_Path
        FROM    @TABLE
        WHERE   Main_Cat_Id IS NULL
        UNION ALL
        SELECT  t.*,
        r.ID_Path + CAST(t.cat_id AS VARCHAR(MAX)) + '\'
        FROM    @TABLE t INNER JOIN
                Recursives r    ON  t.Main_Cat_Id = r.cat_id
)
SELECT  *
FROM    Recursives