SqlServer使用公用表表达式（CTE）实现无限级树形构建

SQL Server 2005开始，我们可以直接通过CTE来支持递归查询,CTE即公用表表达式

公用表表达式（CTE），是一个在查询中定义的临时命名结果集将在from子句中使用它。每个CTE仅被定义一次（但在其作用域内可以被引用任意次），并且在该查询生存期间将一直生存。可以使用CTE来执行递归操作。

DECLARE @Level INT=3

;WITH cte_parent(CategoryID,CategoryName,ParentCategoryID,Level)
AS
(
 SELECT category_id,category_name,parent_category_id,1 AS Level
 FROM TianShenLogistic.dbo.ProductCategory WITH(NOLOCK)
WHERE category_id IN
(
SELECT category_id
FROM TianShenLogistic.dbo.ProductCategory
WHERE parent_category_id=0
)
 UNION ALL
 SELECT b.category_id,b.category_name,b.parent_category_id,a.Level+1 AS Level
 FROM TianShenLogistic.dbo.ProductCategory b
 INNER JOIN cte_parent a
 ON a.CategoryID = b.parent_category_id
)

SELECT
CategoryID AS value,
CategoryName as label,
ParentCategoryID As parentId,
Level
FROM cte_parent WHERE Level <=@Level;
public static List<LogisticsCategoryTreeEntity> GetLogisticsCategoryByParent(int? level)
   {
     if (level < 1) return null;

var dataResult = CategoryDA.GetLogisticsCategoryByParent(level);
     var firstlevel = dataResult.Where(d => d.level == 1).ToList();
     BuildCategory(dataResult, firstlevel);
     return firstlevel;
   }

private static void BuildCategory(List<LogisticsCategoryTreeEntity> allCategoryList, List<LogisticsCategoryTreeEntity> categoryList)
   {
     foreach (var category in categoryList)
     {
       var subCategoryList = allCategoryList.Where(c => c.parentId == category.value).ToList();
       if (subCategoryList.Count > 0)
       {
         if (category.children == null) category.children = new List<LogisticsCategoryTreeEntity>();
         category.children.AddRange(subCategoryList);
         BuildCategory(allCategoryList, category.children);
       }
     }
   }

来源：http://leelei.blog.51cto.com/856755/1957792