Question

所以这是一个学校作业。我不明白为什么我的SQL查询返回它的数字。我创建了8个表。感兴趣的主要是学生

CREATE TABLE    Student
(
    Number  INT     NOT NULL    IDENTITY(130001, 1),
    Name    CHAR(55)    NOT NULL,

    PRIMARY KEY (Number)
)

我已经插入了36个名字（因为这是我们有多少学生）。但是当我运行查询时

SELECT COUNT(Student.Name) AS 'Total number of students'
FROM Student

它返回144.我想说这与给定的代码有关。

DECLARE @totalProgram   INT
DECLARE @totalStudent   INT
DECLARE @i              INT

SET @totalProgram = (SELECT COUNT(*) FROM Program)
SET @totalStudent = (SELECT COUNT(*) FROM Student)
SET @i = 1

WHILE @i <= @totalStudent
    BEGIN
    INSERT INTO ProgramGraduate
        (
            ProgramID, 
            StudentNumber
        )
        VALUES
        (
            FLOOR(RAND() * @totalProgram + 1),
            FLOOR(RAND() * @totalStudent + 130001)
        )
    SET @i = @i + 1
    END
GO

我认为它的目的是随机化一个项目的学生总数？我理解前6行是声明变量并为变量赋值，但是当WHILE循环开始时，我感到困惑。如果您想帮助我剖析一下了解代码中发生了什么，我真的很感激。谢谢！

汉娜

Answer 1

DECLARE @totalProgram   INT   --<-- Declaration of variables
DECLARE @totalStudent   INT
DECLARE @i              INT

SET @totalProgram = (SELECT COUNT(*) FROM Program) --<-- @totalProgram storing total number of rows in Program table 
SET @totalStudent = (SELECT COUNT(*) FROM Student) --<-- @totalStudent storing total number of rows in Student table 
SET @i = 1                                        --<-- Hardcoding value to 1

WHILE @i <= @totalStudent    --<-- "While loop Condition" Execute this while until value of @i is Less than or equal to the value of  @totalStudent
    BEGIN
    INSERT INTO ProgramGraduate      --<-- Insert Statement for the ProgramGraduate table 
        (
            ProgramID,                 --<-- Column Name 1
            StudentNumber               --<-- Column Name 2
        )
        VALUES
        (
            FLOOR(RAND() * @totalProgram + 1),          --<-- Generating a Random Number Between 1 and @totalProgram
            FLOOR(RAND() * @totalStudent + 130001)      --<-- Generating a Random Number Between 130001 and @totalStudent 
        )
    SET @i = @i + 1    --<-- Increasing the value of @i by one everytime this loop executes "Eventually to make the while loop condition ture and break the loop otherwise it will be an idefinite loop"
    END
GO

SQL结果没有意义？

1 个答案: