Insert语句不会插入Null值 [英] Insert statement won't insert Null value

问题描述

我试图插入一个空值在C＃中像这样我的数据库：

I'm trying to insert a null value into my database from C# like this:

SqlCommand command = new SqlCommand("INSERT INTO Employee
VALUES ('" + employeeID.Text + "','" + name.Text + "','" + age.Text
        + "','" + phone.Text + "','" + DBNull.Value + "')", connection);

DBNull.Value就是一个日期可以，但我想它是等于空，但它似乎把一个默认日期1900年什么......

DBNull.Value is where a date can be but I would like it to be equal to null but it seems to put in a default date, 1900 something...

推荐答案

更改为：

SqlCommand command = new SqlCommand("INSERT INTO Employee VALUES ('" + employeeID.Text + "','" + name.Text + "','" + age.Text + "','" + phone.Text + "',null)", connection);

DBNull.Value.ToString（）返回空字符串，但你要null替代。

DBNull.Value.ToString() returns empty string, but you want null instead.

然而，这建立查询可能会导致问题的方式。例如，如果你的一个字符串包含引号'生成的查询将抛出错误。更好的方法是使用参数和SqlCommand对象上设置：

However this way of building your query can lead to issues. For example if one of your strings contain a quote ' the resulting query will throw error. A better way is to use parameters and set on the SqlCommand object:

SqlCommand command = new SqlCommand("INSERT INTO Employee VALUES (@empId,@name,@age,@phone,null)", connection);
command.Parameters.Add(new SqlParameter("@empId", employeeId.Text));
command.Parameters.Add(new SqlParameter("@name", name.Text));
command.Parameters.Add(new SqlParameter("@age", age.Text));
command.Parameters.Add(new SqlParameter("@phone", phone.Text));

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