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通常用來實現樹形結構

首先來看一下表數據

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?以下代碼是遞歸查詢北京市的樹結構

WITH org AS (SELECT Code, name, parentCode, 1 AS levelFROM TestCity WHERE code = '01'UNION ALLSELECT t1.Code, t1.name, t1.parentCode, t2.level + 1 AS levelFROM TestCity t1 INNER JOIN org t2ON t1.parentCode = t2.Code ) SELECT * FROM org

　　

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注意：如果要在with表達式中計算，需要保證兩邊的type一致，如

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WITH org AS (SELECT Code, name, parentCode, 1 AS level, tname = CAST('' as nvarchar(20))FROM TestCity WHERE code = '01'UNION ALLSELECT t1.Code, t1.name, t1.parentCode, t2.level + 1 AS level, tanme = CAST(N'|--' + t2.tname as nvarchar(20))FROM TestCity t1 INNER JOIN org t2ON t1.parentCode = t2.Code ) SELECT code ,parentCode, tname + name as name FROM org

　　

再比較以下兩段從StackOverFolw中摘來的代碼

--報錯 Types don't match between the anchor and the recursive part in column "nm" of recursive query "cte". WITH cte AS (SELECT 1 as rn, 'name1' as nmUNION ALLSELECT rn + 1,nm = 'name' + CAST((rn + 1) as varchar(255))FROM cte a WHERE rn < 10) SELECT * FROM cte--正解 with cte as ( select 1 as rn, CAST('name1' AS VARCHAR(255)) as nm union all select rn+1,nm = CAST('name' + CAST((rn+1) as varchar(255)) AS VARCHAR(255)) from cte a where rn<10) select * from cte

　　

轉載于:https://www.cnblogs.com/guangmangchen/p/6688883.html

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