Question

我有两张桌子;类别和产品。对于每个类别，我想计算其所有子类别中有多少产品。我已经计算了每个类别中有多少。示例表是：

分类

ID  ParentID  ProductCount  SubCategoryProducts
1   NULL      0
2   1         2
3   2         1

产品：

ProductID  CategoryID
123        2
124        2
125        3

所以我想要我的功能：

ID  ParentID  ProductCount  SubCategoryProducts
1   NULL      0             3
2   1         2             1
3   2         1             0

它只需要作为选择查询，无需更新数据库。

有什么想法吗？

编辑：SQL FIddle：http://sqlfiddle.com/#!2/1941a/4/0

Answer 1

如果是我，我会创建一个存储过程。另一个选择是通过第一个查询循环PHP，然后为每个ID运行另一个查询 - 但这种逻辑可以大大减慢您的页面速度。

这是一个很好的存储过程教程：http://net.tutsplus.com/tutorials/an-introduction-to-stored-procedures/

基本上你运行我上面提到的与PHP相同的循环（但它运行得更快）。该过程存储在数据库中，可以像函数一样调用。结果与查询相同。

根据要求，这是一个示例程序（或者更确切地说，它使用了两个）在我的实例中，“ags_orgs”的行为方式类似于有parentOrgID的类别。 “getChildOrgs”也有点像冗余函数，因为我不知道我必须去多少级别（这是为MSSQL编写的 - 可能与mySQL存在差异）不幸的是，这不计算行数，而是获取数据。我强烈建议您按照一两个教程来更好地掌握它的工作原理：

USE [dbname]
GO

/****** Object:  StoredProcedure [dbo].[getChildOrgs]    Script Date: 09/26/2012 15:30:06 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE PROCEDURE [dbo].[getChildOrgs]

@myParentID int,
@isActive tinyint = NULL

AS
BEGIN

    SET NOCOUNT ON
    DECLARE @orgID int, @orgName varchar(255), @level int

        DECLARE cur CURSOR LOCAL FOR SELECT orgID FROM dbo.ags_orgs WHERE parentOrgID = @myParentID AND isActive = ISNULL(@isActive, isActive) ORDER BY orderNum, orgName


    OPEN cur
        fetch next from cur into @orgID
    WHILE @@fetch_status = 0
    BEGIN
        INSERT INTO #temp_childOrgs SELECT orgID,orgName,description,parentOrgID,adminID,isActive,@@NESTLEVEL-1 AS level  FROM dbo.ags_orgs WHERE orgID = @orgID

        EXEC getChildOrgs @orgID, @isActive
        -- get next result
        fetch next from cur into @orgID
    END
    CLOSE cur
    DEALLOCATE cur

END

GO

这个过程称为

USE [dbname]
GO

/****** Object:  StoredProcedure [dbo].[execGetChildOrgs]    Script Date: 09/26/2012 15:29:34 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE PROCEDURE [dbo].[execGetChildOrgs]

@parentID int,
@isActive tinyint = NULL,
@showParent tinyint = NULL

AS

BEGIN

CREATE TABLE #temp_childOrgs
(
   orgID int,
   orgName varchar(255),
   description text,
   parentOrgID int,
   adminID int,
   isActive tinyint,
   level int
)
-- if this isn't AGS top level (0), make the first record reflect the requested organization
IF @parentID != 0 AND @showParent = 1
BEGIN
    INSERT INTO #temp_childOrgs SELECT orgID,orgName,description,parentOrgID,adminID,isActive,0 AS level  FROM dbo.ags_orgs WHERE orgID = @parentID
END

exec getChildOrgs @parentID, @isActive

SELECT * FROM #temp_childOrgs
DROP TABLE #temp_childOrgs
END

GO

Answer 2

如果您对层次结构的深度有限制，则可以在一个语句中执行此操作。你说你总共只有4级。

SELECT SUM(ProductCount)
FROM (
    SELECT c0.ID, c0.ProductCount
    FROM Categories AS c0
    WHERE c0.ID = 1
    UNION ALL
    SELECT c1.ID, c1.ProductCount
    FROM Categories AS c0
    JOIN Categories AS c1 ON c0.ID = c1.ParentID
    WHERE c0.ID = 1
    UNION ALL
    SELECT c2.ID, c2.ProductCount
    FROM Categories AS c0
    JOIN Categories AS c1 ON c0.ID = c1.ParentID
    JOIN Categories AS c2 ON c1.ID = c2.ParentID
    WHERE c0.ID = 1
    UNION ALL
    SELECT c3.ID, c3.ProductCount
    FROM Categories AS c0
    JOIN Categories AS c1 ON c0.ID = c1.ParentID
    JOIN Categories AS c2 ON c1.ID = c2.ParentID
    JOIN Categories AS c3 ON c2.ID = c3.ParentID
    WHERE c0.ID = 1
) AS _hier;

如果以您正在进行的方式存储层次结构，那么这将适用于此查询，称为邻接列表。基本上，ParentID是每个节点记录其在层次结构中的位置的方式。

还有一些其他存储层次结构的方法可以更容易地查询整个树或子树。最佳数据组织取决于您要运行的查询。

以下是更多资源：

Models for Hierarchical Data with SQL and PHP（用户@ RaymondNijland在评论中链接到它）
我将该演示文稿作为webinar（可以自由查看录制内容，但需要注册）。
我的书SQL Antipatterns: Avoiding the Pitfalls of Database Programming。
What is the most efficient/elegant way to parse a flat table into a tree?

Answer 3

这是我计算所有子类别中产品的过程

DELIMITER $$
CREATE PROCEDURE CountItemsInCategories(IN tmpTable INT, IN parentId INT, IN updateId INT)
BEGIN

    DECLARE itemId INT DEFAULT NULL;
    DECLARE countItems INT DEFAULT NULL;
    DECLARE done INT DEFAULT FALSE;
    DECLARE recCount INT DEFAULT NULL;

    DECLARE 
        bufItemCategory CURSOR FOR
    SELECT
        itemCategory.id AS id,
        COUNT(CASE WHEN item.isVisible = 1 then 1 ELSE NULL END) items
    FROM
        itemCategory
    LEFT JOIN item ON
        item.categoryId = itemCategory.id 
    WHERE
        itemCategory.isVisible = 1 AND itemCategory.categoryParentId = parentId 
    GROUP BY
        itemCategory.id
    ORDER BY
        itemCategory.name;

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

    SET max_sp_recursion_depth = 10000;

    IF tmpTable = 1 THEN
        DROP TEMPORARY TABLE IF EXISTS tblResults;
        CREATE TEMPORARY TABLE IF NOT EXISTS tblResults(
            id INT NOT NULL PRIMARY KEY,
            items INT
        );
    END IF;

    OPEN bufItemCategory;

        Reading_bufItemCategory: LOOP

            FETCH FROM bufItemCategory INTO itemId, countItems;

            IF done THEN
                LEAVE Reading_bufItemCategory;
            END IF;

            IF tmpTable = 1 THEN
                INSERT INTO tblResults VALUES(itemId, countItems);
            ELSE
                UPDATE tblResults SET items = items + countItems WHERE id = updateId;
            END IF;

            SET recCount = (SELECT count(*) FROM itemCategory WHERE itemCategory.categoryParentId = itemId AND itemCategory.isVisible = 1);

            IF recCount > 0 THEN
                CALL CountItemsInCategories(0, itemId, CASE WHEN updateId = 0 then itemId ELSE updateId END);
            END IF;

        END LOOP Reading_bufItemCategory;

    CLOSE bufItemCategory;

    IF tmpTable = 1 THEN
        SELECT * FROM tblResults WHERE items > 0;
        DROP TEMPORARY TABLE IF EXISTS tblResults;
    END IF;

END $$
DELIMITER;

要调用过程，只需运行：

CountItemsInCategories(firstLoop,parentId,updateId);

其中的参数是：

firstLoop-首次循环始终为“ 1”

parentId-子类别的父项

updateId-要更新的行的ID，第一次循环时始终为“ 0”

例如：

CountItemsInCategories(1,1,0);

我希望这个例子对某人有用。

Answer 4

这假设您有产品表名为 prods

prod_id|categ_id

和名为 categ

的类别表

categ_id|parent_categ_id

您似乎正在使用邻接表结构，其中外键 parent_categ_id 列引用同一张表中的 prod_id 列以下查询应该有效

select c1.categ_id,c1.parent_categ_id,count(prods.prod_id)
as product_count from categ c1
join prods on prods.categ_id=c1.categ_id or prods.categ_id
    in( with recursive tree(id,parent_id)as 
    (select categ_id,parent_categ_id from categ 
    where categ_id=c1.categ_id  
    union all
    select cat.categ_id,cat.parent_categ_id from categ cat
    join tree on tree.id=cat.parent_categ_id) select id from tree)
group by c1.categ_id,c1.parent_categ_id 
order by product_count

MySQL计算所有子类别的产品

4 个答案: