Sql server 带条件插入的存储过程

我试图用

If

语句编写一个过程

这是我的数据库

我的想法是：当我们有相同的

ComandmentNumber

时，

StudentNumber

必须增加1，但当我们有新的

ComandmentNumber

时，

StudentNumber

必须从1开始

例如：

下面是我在SQL Server中的过程

CREATE PROCEDURE InsertIntoDefeatsGraduates
    @ComandmentNumber VARCHAR(100),
    @StudentFakNumber INT
AS
BEGIN
    DECLARE @StudentNumber INT 

    IF EXISTS (SELECT * FROM dbo.[Defeats-Graduates] 
               WHERE ComandmentNumber = @ComandmentNumber) 
    BEGIN
        SET @StudentNumber += 1

        INSERT INTO dbo.[Defeats-Graduates] (ComandmentNumber, StudentNumber, StudentFakNumber) 
        VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)
    END
    ELSE
    BEGIN
        SET @StudentNumber = 1

        INSERT INTO dbo.[Defeats-Graduates](ComandmentNumber, StudentNumber, StudentFakNumber) 
        VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)
    END
END

但是，当我尝试执行此操作时，会出现以下错误：

无法将值NULL插入“StudentNumber”列中的表“Test.dbo.designs”；列不允许空值。插入失败

---

你从不初始化你的

@StudentNumber

-你只需要声明它-然后它是

NULL

-并且将

+1

添加到

NULL

中仍然保持

NULL

-所以最后，你要尝试将

NULL

插入你的表中

-- at this point, @StudentNumber is NULL 
DECLARE @StudentNumber INT 

IF EXISTS (SELECT * FROM dbo.[Defeats-Graduates] 
           WHERE ComandmentNumber = @ComandmentNumber) 
BEGIN
    -- trying to increment a NULL value still results in NULL
    SET @StudentNumber += 1

    -- here you're about to insert NULL into "StudentNumber"
    INSERT INTO dbo.[Defeats-Graduates] (ComandmentNumber, StudentNumber, StudentFakNumber) 
    VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)

您需要做的是读取实际值，如果实际值存在：

IF EXISTS (SELECT * FROM dbo.[Defeats-Graduates] 
           WHERE ComandmentNumber = @ComandmentNumber) 
BEGIN
    -- get the highest value and increment by one
    SELECT @StudentNumber = MAX(StudentNumber) + 1
    FROM dbo.[Defeats-Graduates] 
    WHERE ComandmentNumber = @ComandmentNumber;

---

请注意：如果系统繁忙，且多个客户端同时工作和插入数据，

SELECT MAX（）+1

方法非常容易产生重复值。只要有可能，您应该使用适当的数据库提供的机制—类似于SQL Server中的

序列

，或类似的机制，其设计和构建旨在提供独特的值，即使在繁重的工作负荷下。

你也不会初始化你的

@StudentNumber

-你只需声明它-然后它就是

NULL

-并且将

+1

添加到

NULL

中仍然保持

NULL

-所以最后，你试图将

NULL

插入你的表中

-- at this point, @StudentNumber is NULL 
DECLARE @StudentNumber INT 

IF EXISTS (SELECT * FROM dbo.[Defeats-Graduates] 
           WHERE ComandmentNumber = @ComandmentNumber) 
BEGIN
    -- trying to increment a NULL value still results in NULL
    SET @StudentNumber += 1

    -- here you're about to insert NULL into "StudentNumber"
    INSERT INTO dbo.[Defeats-Graduates] (ComandmentNumber, StudentNumber, StudentFakNumber) 
    VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)

您需要做的是读取实际值，如果实际值存在：

IF EXISTS (SELECT * FROM dbo.[Defeats-Graduates] 
           WHERE ComandmentNumber = @ComandmentNumber) 
BEGIN
    -- get the highest value and increment by one
    SELECT @StudentNumber = MAX(StudentNumber) + 1
    FROM dbo.[Defeats-Graduates] 
    WHERE ComandmentNumber = @ComandmentNumber;

---

请注意：如果系统繁忙，且多个客户端同时工作和插入数据，

SELECT MAX（）+1

方法非常容易产生重复值。只要有可能，您应该使用适当的数据库提供的机制—类似于SQL Server中的

序列

，或类似的机制，其设计和构建旨在提供独特的值，即使在繁重的工作负荷下。

对于

@StudentNumber

，您也没有作业说明。在第一种情况下，您可以尝试以下方法：

CREATE PROCEDURE InsertIntoDefeatsGraduates
    @ComandmentNumber VARCHAR(100),
    @StudentFakNumber INT
AS
BEGIN
    DECLARE @StudentNumber INT 
    SELECT @StudentNumber = StudentNumber  FROM dbo.[Defeats-Graduates] 
               WHERE ComandmentNumber = @ComandmentNumber
    IF ISNULL(@StudentNumber, 0) > 0
      BEGIN
        SET @StudentNumber += 1

        INSERT INTO dbo.[Defeats-Graduates] (ComandmentNumber, StudentNumber, StudentFakNumber) 
        VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)
      END
    ELSE
      BEGIN
        SET @StudentNumber = 1

        INSERT INTO dbo.[Defeats-Graduates](ComandmentNumber, StudentNumber, StudentFakNumber) 
        VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)
      END
    END

---

您没有

@StudentNumber

的赋值语句。在第一个条件中，您可以尝试以下操作：

CREATE PROCEDURE InsertIntoDefeatsGraduates
    @ComandmentNumber VARCHAR(100),
    @StudentFakNumber INT
AS
BEGIN
    DECLARE @StudentNumber INT 
    SELECT @StudentNumber = StudentNumber  FROM dbo.[Defeats-Graduates] 
               WHERE ComandmentNumber = @ComandmentNumber
    IF ISNULL(@StudentNumber, 0) > 0
      BEGIN
        SET @StudentNumber += 1

        INSERT INTO dbo.[Defeats-Graduates] (ComandmentNumber, StudentNumber, StudentFakNumber) 
        VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)
      END
    ELSE
      BEGIN
        SET @StudentNumber = 1

        INSERT INTO dbo.[Defeats-Graduates](ComandmentNumber, StudentNumber, StudentFakNumber) 
        VALUES (@ComandmentNumber, @StudentNumber, @StudentFakNumber)
      END
    END

---

不，在这种情况下，

@StudentNumber

已经有一个大于0的值。实际上，

从dbo中选择@StudentNumber=StudentNumber。[击败毕业生]其中ComandmentNumber=@ComandmentNumber

将初始化

@StudentNumber

，如果任何记录匹配。不，在这种情况下，

@StudentNumber

已经有一个大于0的值。实际上，

从dbo中选择@StudentNumber=StudentNumber。[击败毕业生]其中，如果有任何记录匹配，ComandmentNumber=@ComandmentNumber

将初始化

@StudentNumber

。