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  • WITH common_table_expression

    Feature:
    • 公用表表达式只能包含一个SELECT,多SELECT需UNION,UNION ALL
    • 公用表表达式只能引用一次
    • 公用表表达式可以包括对自身的引用,这种表达式称为递归公用表表达式
    --临时表变量
    WITH t_Class
    AS
    (
        SELECT *
        FROM Intranet..TemplateDocClass
        WHERE State = 1
    )
    SELECT COUNT(1)
    FROM t_Class
    
    --引用自身,递归多级别
    WITH t_Class
    AS
    (
        SELECT ID,ClassName,1 AS [Deep]
        FROM Intranet..TemplateDocClass
        WHERE ParentID = -1
    
        UNION ALL
    
        SELECT C1.ID,C1.ClassName,C2.Deep + 1
        FROM Intranet..TemplateDocClass AS C1
        INNER JOIN t_Class AS C2 ON C2.ID = C1.ParentID
    )
    SELECT *
    FROM t_Class
     
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  • 原文地址:https://www.cnblogs.com/zenple/p/4830043.html
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