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string Users = "select UserId from Users where Name=" + User.Identity.Name;

What I have tried:

Actually all solution who i try don't not succes
Updated 21-Nov-22 21:25pm

1 solution

You don't put data into a DB with a SELECT statement - that fetches data from the DB.
To add new data, you use an INSERT: SQL INSERT INTO Statement[^]
To change existing data, you use an UPDATE: SQL UPDATE Statement[^]

Either way, you need to use a parameterized query: 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:
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:
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'
Which SQL sees as three separate commands:
SELECT * FROM MyTable WHERE StreetAddress = 'x';
A perfectly valid SELECT
A perfectly valid "delete the table" command
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?

using (SqlConnection con = new SqlConnection(strConnect))
    using (SqlCommand cmd = new SqlCommand("INSERT INTO myTable (myColumn1, myColumn2) VALUES (@C1, @C2)", con))
        cmd.Parameters.AddWithValue("@C1", myValueForColumn1);
        cmd.Parameters.AddWithValue("@C2", myValueForColumn2);
Share this answer
Kuepo David giress 22-Nov-22 3:54am    
I manage to retrieve the name of the user to connect and I would like to display the tasks according to this name, which is why I wanted to make a query concatenate to a variable
OriginalGriff 22-Nov-22 4:18am    
Then why are you talking about adding data to a database?
Richard Deeming 22-Nov-22 4:32am    
Griff's solution still stands: if you concatenate the parameter value directly into the query, rather than use a properly parameterized query, then your code is vulnerable to SQL Injection[^]. You won't have to wait long until it is accidentally or deliberately destroyed by a visit from Bobby Tables[^].

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