Search problem on visual studio and SQL

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Hi,I have this search problem with such error, Help?
(I use visual studio ultimate 2013 & SQL Server 2014 Management Studio):

An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll

Additional information: Incorrect syntax near the keyword 'Like'.

This is my SEARCH function:

C#

public static void SEARCH(DataGridView dtg, int I)
        {

            String SQL = "";
            UInt64 Where = 0;
            SQL = " Select  nam as[Name], fam as[Family name], fat as[Father name], nat[ID code], cel as[Cell.], tel as[Tell.], [add] as[Address] From newuser ";
            if (I == 0)
            {
                SQL = SQL + " where ";
            }
            if (I != 0)
            {
                if (Where == 0)
                {
                    Where = 1;
                }
                else
                {
                    SQL = SQL + " And ";
                }
                SQL = SQL + "I Like %" + I + "% ";

            }



            dtg.DataSource = DataBase.ExecuteSelect(SQL);



        }

And this is how I return it in my search button:

 int ID;

            ID = 0;
            ID = Convert.ToInt32(txtuserID.Text);


            newuser.SEARCH(dtgfs, ID);

What I have tried:

well I not sure what to do so I would if you can help me.
(I use visual studio ultimate 2013 & SQL Server 2014 Management Studio).

Posted 5-Aug-19 20:40pm

User 14118045

Updated 5-Aug-19 21:27pm

OriginalGriff

v2

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Comments

Richard MacCutchan 6-Aug-19 3:24am

Check the contents of the final SQL string to see what is missing or mis-quoted after the Like clause. Also what is the data type of the I field in the database?

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OriginalGriff · Answer 1 · 2019-08-05T21:27:00

First off, Like is expecting a string, so you would need to send this to SQL:

SQL

SELECT ... WHERE MyColumn LIKE '%matchthis%'

To get rid of your error.
However, that looks very wrong: if I is zero, your SQL will end up as:

SQL

SELECT ... WHERE

with no condition, and if it isn't you will get either

SQL

SELECT ... I LIKE ...

Which is missing the WHERE or

SQL

SELECT ... AND I LIKE ...

Which is missing the WHERE and the initial condition!
I'd strongly suggest you learn to use the debugger and look directly at the strings you are generating, because they aren't going to work...

But ... Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'

The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'

Which SQL sees as three separate commands:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';

A perfectly valid SELECT

SQL

DROP TABLE MyTable;

A perfectly valid "delete the table" command

SQL

--'

And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?