BI - SQL 丨 WHILE

WHILE

WHILE, the meaning of when.In the syntax of SQL, it can usually be used to repeatedly execute a certain SQL script.

In layman's terms, when XXX, execute a certain operation, which means a cycle.

Seeing this, friends may have questions, is there a similar operation in PowerBI?

The answer is yes, but we generally perform such operations in PowerQuery, and there are fewer scenarios that require loop processing in DAX.

In SQL, there are many scenarios that need to be processed using loop statements, such as data update or incremental calculation.

Syntax

WHILE conditional judgmentBEGINperform actionSET @[email protected]+1 -- parameter cycle incrementsEND

Note:

If two or more WHILE loops are nested, all statements up to the end of the inner loop are run first, and then the execution of the next outer loop resumes.

Use examples

Case data:

There is a database named "CaseData" in the database of the white tea machine.

"Dim_Date" date table, "Dim_Product" product table, "Fact_Sales" sales fact table.

Example 1:

Loop printing numbers, from 1 to 9.

DECLARE @NUM INT;SET @NUM = 1;WHILE @NUM<= 9BEGINPRINT @NUMSET @NUM = @NUM + 1;END

The results are as follows:

Note: This operation cannot be performed in PowerBI, and an error will be reported.

Example 2:

Create a table and insert ProductName and Price whose Price is less than or equal to 10 in a loop.

USE CaseDataCREATE TABLE BaiCha(Pname VARCHAR(50),Prict INT)

Create a table first, the result is as follows:

p>

Execute the following statement:

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

The result is as follows:

Let's take a look at the data:

You can see that the product information whose price is less than or equal to 10 has been inserted into the target table.

Example 3:

Using a double loop, calculate the square of 1 to 9.

USE CaseDataDECLARE @NUM1 INT,@NUM2 INT ,@NUM3 VARCHAR(10);SET @NUM1=1;WHILE @NUM1<= 9BEGINSET @NUM2=1WHILE @NUM2<[email protected] @[email protected]*@NUM1SET @[email protected]+1ENDPRINT @NUM3SET @[email protected]+1END

The results are as follows:

Minor bug tips:

There are often small partners who are confused when they write in a loop, the execution cycle cannot be ended, and no results are displayed. In this case, it is necessary to check the incremental SET in BEGIN to see if it is due to failure.Set increment results.

Here is Bai Cha, a beginner in PowerBI.