BI-SQL丨WHILE

WHILE

WHILE,when it means.在SQL的语法中,Often used to repeat a sectionSQL脚本.

通俗来说,就是当XXX时,执行某某操作,意为循环.

看到这里,小伙伴可能会有疑问,PowerBIIs there a similar operation in ？

答案是有的,But we usually do this kind of thingPowerQuery中进行的,在DAXThere are fewer scenarios in which loop processing is required.

而在SQL中,There are many scenarios that need to be handled with a loop statement,Such as data update or incremental calculation.

语法

WHILE 条件判断
BEGIN 
执行操作 
SET @[email protected]+1 --The parameters are incremented cyclically
END 

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注意：

If two or more are nested WHILE 循环,All statements up to the end of the inner loop are run first,然后下一个外层循环重新开始执行. 

使用实例

案例数据：

在白茶本机的数据库中存在名为“CaseData”的数据库.

“Dim_Date“日期表、"Dim_Product"产品表、"Fact_Sales"销售事实表.

例子1：

循环打印数字,从1到9.

DECLARE @NUM INT;
SET @NUM = 1;   
WHILE @NUM<= 9
BEGIN
   PRINT @NUM
   SET @NUM = @NUM + 1;
END

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结果如下：

注：This operation is not availablePowerBI中执行,会有报错.

例子2：

创建一张表,and loop through the table insertsPrice小于等于10的ProductName和Price.

USE CaseData
CREATE TABLE BaiCha
(Pname VARCHAR(50),
Prict INT
)

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先创建一张表,结果如下：

执行以下语句：

USE CaseData
DECLARE @NUM INT;
SET @NUM=1
WHILE @NUM<= 10
BEGIN
   INSERT INTO BaiCha(Pname,Prict) 
   SELECT ProductName AS T1,Price AS T2 FROM Dim_Product WHERE [email protected]
   SET @NUM = @NUM + 1;
END

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结果如下：

我们来查看一下数据：

可以看到,价格小于等于10The product information has been inserted into the target table.

例子3：

利用双层循环,计算1到9的平方.

USE CaseData
DECLARE @NUM1 INT,@NUM2 INT ,@NUM3 VARCHAR(10);
SET @NUM1=1;
WHILE @NUM1<= 9 
BEGIN
    SET @NUM2=1
    WHILE @NUM2<[email protected]
    BEGIN
    SET @[email protected]*@NUM1
    SET @[email protected]+1
    END
PRINT @NUM3
SET @[email protected]+1
END

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结果如下：

小Bug提示：There are often small partners who write and write in a loop and then get confused,The execution loop cannot end,Also no results are displayed,这种情况下,需要对BEGINIncrement insideSET进行检测,See if it is caused by not setting the increment.

这里是白茶,一个PowerBI的初学者.