SQL WHILE循环 [英] SQL WHILE Loops

问题描述

我一直在努力在SQL中创建嵌套的while循环，但是while循环有问题.我认为主要问题在于我的外部循环.有什么建议?

I have been working on creating a nested while loop in SQL, but having issues with the while loop. I think the main issue is with my outer loop. Any suggestions?

USE HW_DB;
IF OBJECT_ID('dbo.PythagoreanTriangles') IS NOT NULL
    DROP TABLE dbo.PythagoreanTriangles;
GO

CREATE TABLE PythagoreanTriangles
(
    Side1 INT NOT NULL,
    Side2 INT NOT NULL,
    Hypotenuse FLOAT NOT NULL
);

DECLARE @side1 AS INT = 1;
DECLARE @side2 AS INT = 1;
DECLARE @count AS INT = 1;
DECLARE @element  AS INT = 0;

WHILE (@side1 = @count) 
    BEGIN
        WHILE @side2 <= 10 BEGIN
            INSERT INTO dbo.PythagoreanTriangles
                VALUES (@side1, @side2, SQRT((@side2 * @side2) + (@side1 * @side1)));
            UPDATE dbo.PythagoreanTriangles SET Hypotenuse = ROUND(Hypotenuse, 2)

        SET @side2 = @side2 + 1;
        SET @count = @count + 1;
        SET @element = @element + 1;

    IF @element = 10
    BEGIN 
    SET @side1 = @side1 + 1;
    SET @element = 0;

END;
END;
END;

输出应如下所示:

1 1 1.41
1 2 2.24
1 3 ...
1 4 ...
1 5
1 6
1 7
1 8
1 9
1 10
2 2
2 3
2 4
2 5
2 6
2 7
2 8
2 9
2 10
.....
........等

1 1 1.41
1 2 2.24
1 3 ...
1 4 ...
1 5
1 6
1 7
1 8
1 9
1 10
2 2
2 3
2 4
2 5
2 6
2 7
2 8
2 9
2 10
..........
........ etc

9 9
9 10
10 10

9 9
9 10
10 10

推荐答案

您可以通过一次插入操作来完成此操作，在可能的情况下，我始终建议您避免使用循环/游标.

You can do this with a single insert, and where possible I would always advise avoiding loops/cursors.

WITH Numbers AS
(   SELECT  TOP 10 Number = ROW_NUMBER() OVER(ORDER BY object_id)
    FROM    sys.all_objects
)
INSERT dbo.PythagoreanTriangles (Side1, Side2, Hypotenuse)
SELECT  Side1 = a.Number, 
        Side2 = b.Number,
        Hypotenuse = ROUND(SQRT(POWER(a.Number, 2) + POWER(b.Number, 2)), 2)
FROM    Numbers a
        CROSS JOIN Numbers b;

关于SQL Fiddle的示例

Example on SQL Fiddle

尽管实际上可以回答您的问题，但由于存在以下情况，循环会在一次迭代后退出:

Although to actually answer your question, your loop exits after one iteration because you have this condition:

WHILE (@side1 = @count) 

在@ side2 1-10的第一次迭代之后，执行SET @side1 = @side1 + 1;.由于@Count = 1和@Side1现在为2，因此您的WHILE谓词不再为true，因此外部循环退出.尽管我不主张使用这种方法，但是要使循环正常工作，您需要在谓词期间更改外部.也许像这样:

After the first iteration of @side2 1 - 10, you do SET @side1 = @side1 + 1;. Since @Count = 1, and @Side1 is now 2, your WHILE predicate is no longer true, so the outer loop exits. Although I don't advocate this approach, to make your loop work, you would need to change your outer while predicate. Perhaps something like:

DECLARE @side1 AS INT = 1;
DECLARE @side2 AS INT = 1;

WHILE (@side1 <= 10) 
    BEGIN
        WHILE @side2 <= 10 
            BEGIN
                INSERT INTO dbo.PythagoreanTriangles
                    VALUES (@side1, @side2, SQRT((@side2 * @side2) + (@side1 * @side1)));
                UPDATE dbo.PythagoreanTriangles SET Hypotenuse = ROUND(Hypotenuse, 2)

                SET @side2 = @side2 + 1;
            END;

            SET @side2 = 1;
            SET @side1 = @side1 + 1;
    END;

关于SQL Fiddle的示例

Example on SQL Fiddle

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