SQL WHILE循环

admin

SQL WHILE循环

sql

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？

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

9 9
9 10
10 10

阅读 341

2021-06-07

共1个答案

admin

您可以通过单个插入来执行此操作，并且在可能的情况下，我始终建议您避免使用循环/光标。

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;

SQL小提琴上的示例

尽管实际上是要回答您的问题，但由于存在以下情况，因此循环会在一次迭代后退出：

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，@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：

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;

SQL的示例

2021-06-07