C Prevent SQL injection, when typing, there will be more than three errors, indicating that it can n

First of all, your question: declare an integer variable as a counter, judge the counter before each input, if the counter is less than 3, then allow the input, and let the counter increment by 1, if the counter is greater than 3, it will prompt that it can not be entered again.

int i=0;

if(i<3)

Input is allowed. i++;else

Prompt: Cannot be entered.

I suspect that your understanding of SQL injection is biased, the so-called SQL injection does not refer to the insertion of a large amount of data into the database, but refers to the data corruption or leakage caused by injecting query statements into the database. To prevent SQL injection, it is actually very simple, do not directly concatenate query statements, but use SQL parameters to pass parameters. There is a lot of knowledge about this on the Internet, as long as you are interested, you will definitely be able to figure it out.

PS: If you understand SQL injection correctly, then the above way of limiting the number of inputs will not solve the problem at all.

To prevent SQL injection, you don't need to use @name, sqlparameter nameparameter=new sqlparameter("name",name); Is it like this? Do you use it again?

Is it recorded in the data sheet? Probably the reason for the record.

The primary key cannot be empty.

There should be no other problems.

If it doesn't work. Don't forget the primary key.。。 It shouldn't be a very important system, and it can run without a primary key. Just some of the impact on speed.

ODBC Error: [Microsoft][ODBC SQL Server Driver][SQL Server]Create Unique Index terminated because a duplicate key was found that destroys the extremity index ID 1. The most important primary key is the simplified type'12'。

Microsoft][ODBC SQL Server Driver][SQL Server] is not able to create constraints. See the previous error message.

The Microsoft][ODBC SQL Server Driver][SQL Server] statement was terminated.

View the error log.

microsoft sql server\

Find out the cause of the error.

Post the error prompt, and everyone can help you analyze it.

He's already prompted you to look at the log message.,You have to post the content to know what's going on.,I guess the instance name is occupied.。

What is the wrong word? Get the right medicine!

Have you installed SQL before? If you install it, it's useless when you uninstall it.,You need to delete the previously installed ones in the registry.,Otherwise, it's not good.。

Did your machine install SQL before If so, you should delete the files you installed before, don't leave the files, and then delete the files that you haven't installed successfully, restart the computer, and it should be okay to reinstall it, if it still doesn't work, then there should be a problem with the SQL version you installed,

Reinstall the system, don't install the lite version.

The ODBC data source needs to be configured.

--The landlord deletes the login yh before deleting the login yh, he has to delete his database yh before he can delete the login yh

drop user user11

drop login user11

There may be users connected to this db instance, as you can see.

Data is cascaded and cannot be deleted directly.

In the process of installation, you have 15 checks, and you must have passed or not, and as long as one of them fails, it cannot be installed correctly, and all of them must be solved before it can be installed.

You can go to the corresponding online and offline to install it successfully, and then install it again when you pass it, and you can install it normally.

I studied computer science, and I used to install and install this, and similar problems always appeared.

On the one hand, it may be a matter of version, and the SQL that we used to use is, and a few of them are installed anyway, but it doesn't affect the use, like the online series.

On the other hand. That's because SQL is a non-compatible program software, you have installed SQL before, although you uninstall it, but it can't be completely uninstalled, once the system is used, there will be conflicts when installing.

It is recommended that you uninstall it carefully again, uninstall it cleanly, and install it again.

If that doesn't work, it's best to reinstall the system, and it's best to install SQL before installing anything else

if not exists(select @id=id from student where id=@id)

And. if exists(select @id=id from student where id=@id)

The @id==, because you are judging whether there is a value here, not giving the value, when you look at this ** in the query analyzer, there should be a red wavy line below the = of @id=, indicating that there is a problem here.

if exists(select @id=id from student where id=@id)

What do you want? It's the assignment again, and it's the query for whether it exists.

Changed to Yves Exisz (Selekett Edfrom StudentWheelide = @伊德).