SqlServer使用公用表表达式（CTE）实现无限级树形

数据运维 2023-04-21 LOVEHL^ˇ^ 手机阅读

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

                        <p>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</p>

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 GetLogisticsCategoryByParent(int? level) { if (level < 1) return null;

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

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