Question

嘿我试图从我的表中获取缺失值，但我不知道如何在没有CTE和递归的情况下得到它。下面是我目前的代码，但正如我之前所说，它适用于递归。

DROP TABLE #temp;
CREATE TABLE #temp (
    val INT NULL   
);
DECLARE @val AS INT = 1;

WHILE @val <= 10
BEGIN
    INSERT #temp (val)
    SELECT cast((RAND()*10) as int);
    SET @val = @val + 1;
END

SELECT *
FROM   #temp;

WITH CTE AS
(

    SELECT nMin = MIN(t.val), MAX(t.val) as 'nMax' 
    FROM #temp t
    UNION ALL

    SELECT nMin + 1, nMax 
    FROM CTE
    WHERE nMin < nMax
)


SELECT c.nMin
FROM CTE c
WHERE NOT EXISTS
(
    SELECT val
    FROM #temp
    WHERE c.nMin = val
)

Answer 1

您只需要一个没有缺失值的数字列表，这样您就可以进行反连接。

现在，您正尝试使用递归生成这些值。对系统表使用ROW_NUMBER更有效。您可以交叉连接系统表以获取任意数量的数字，并使用TOP子句限制结果。即使在没有用户表的数据库中，也会有系统定义的对象。

我留下了您的代码，以便您可以比较差异。如果你经常使用它，那么在你的数据库中有一个数字表可能是值得的。也称为计数表。

CREATE TABLE #temp (
    val INT NULL   
);
DECLARE @val AS INT = 1;

WHILE @val <= 10
BEGIN
    INSERT #temp (val)
    SELECT cast((RAND()*10) as int);
    SET @val = @val + 1;
END

SELECT *
FROM   #temp ORDER BY val;

WITH CTE AS
(

    SELECT nMin = MIN(t.val), MAX(t.val) as 'nMax' 
    FROM #temp t
    UNION ALL

    SELECT nMin + 1, nMax 
    FROM CTE
    WHERE nMin < nMax
)

,CTE_NUMBERS AS
(
    SELECT TOP(10)
        ROW_NUMBER() OVER(ORDER BY (SELECT 1 as d)) as nMin
    FROM sys.all_objects AS a
    CROSS JOIN sys.all_objects AS b
)

SELECT c.nMin
FROM CTE_NUMBERS c
WHERE NOT EXISTS
(
    SELECT val
    FROM #temp
    WHERE c.nMin = val
)

DROP TABLE #temp

如何在表中查找缺失值

1 个答案: