How to use MySql select with c#

Question

Can anyone tell whats wrong with my code? I have tried a million different things and I cant seem to make it work. I need to make a select in my mysql database and use the id from the table with the specified name I take from a combobox.

I took that name from the combobox and put it into a variable named "nomeres", now I need to do a select with it and take the id from that name from the database. Everything I try to do results in a mysql syntax error in line 1, but I've tried alot of things and its always the same. The database is fine, I tried the select directly from it myself, no tables or columns names are incorrect. This is the code im using:

MySql.Data.MySqlClient.MySqlConnection dbConn = new MySql.Data.MySqlClient.MySqlConnection("Persist Security Info=False;server=localhost;database=notas;uid=root;password=" + dbpwd);

MySqlCommand cmd = dbConn.CreateCommand();
cmd.CommandText = "SELECT id from residentes WHERE nome ='" + nomeres;

try
{
    dbConn.Open();                
} catch (Exception erro) {
    MessageBox.Show("Erro" + erro);
    this.Close();
}

MySqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())
{
    idnumber = reader.ToString();
}

next time you attempt the command, I highly recommend trying the sql command on a test table or, on the real table. Possibly doing this with PHPMyAdmin or something along those lines. — Teddy Codes
– Teddy Codes, Commented Nov 30, 2016 at 16:21

Sudhakar Tillapudi · Accepted Answer · 2013-12-22 04:05:28Z

17

as others have already pointed you towards right direction, i would like to suggest you to use parameterised queries to avoid SQL injection attacks.

Your query is open to SQL injection attacks so please read here

Try This: using parameterised SQL queries

cmd.CommandText = "SELECT id from residentes WHERE nome = @nome";
cmd.Parameters.AddWithValue("@nome",nomeres);

answered Dec 22, 2013 at 4:05

Sudhakar Tillapudi

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3 Comments

Martin Koch Over a year ago

Thx for the tip, but it will be a local application.

Sudhakar Tillapudi Over a year ago

@user3126468: though it is a local application you could use parameterised queries as they also take care of DatTypes to be passed properly.

gregmac Over a year ago

@martin.koch You can still be attacked from someone/something locally. Your code may 'grow up' and end up being used for something bigger and internet-facing. This is how a lot of bad/insecure code gets into production, frankly. Parameters are not difficult to use, and I'd argue they are actually easier as they avoid all the nonsense of escaping values, type conversion, plus your SQL is far more readable.

Gordon Linoff · Accepted Answer · 2013-12-22 03:40:10Z

7

You need to terminate the string in the query:

"SELECT id from residentes WHERE nome ='" + nomeres + "'"

In general, when trying to debug this type of code, it helps to print out the query string after all substitutions have been made.

answered Dec 22, 2013 at 3:40

Gordon Linoff

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4 Comments

Martin Koch Over a year ago

Same error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' SELECT id from residentes WHERE nome ='afslavas'' at line 1

Martin Koch Over a year ago

Btw, it highlights the "MySqlDataReader" line when shows this error. Dont know if that is relevant.

gregmac Over a year ago

Do not do this. This introduces a SQL injection vulnerability, and there's no excuse for not using parameterized queries these days (especially with a library like Dapper). It also will break if you have a literal single quote in your variable.

Gordon Linoff Over a year ago

@gregmac . . . BTW, I agree. You should really be using parameters for the query.

Mulmus Maximus · Accepted Answer · 2023-04-27 12:46:57Z

3

cmd.CommandText = "SELECT id from residentes WHERE nome ='" + nomeres + "';";

Actually you miss the semicolon of the query that have to enter within the quotes. The second semicolon is for the end of statement. But I prefer to write commands like:

 cmd.CommandText = "SELECT id from residentes WHERE nome = @nome";
 cmd.Parameters.AddWithValue("@nome", variableName);

Then execute the query and retrieve your results.

edited Apr 27, 2023 at 12:46

Mulmus Maximus

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answered Jan 15, 2015 at 21:06

NomanJaved

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Comments

Mitch Wheat · Accepted Answer · 2013-12-22 03:41:38Z

1

Missing single quote:

"SELECT id from residentes WHERE nome ='" + nomeres + "'";
                                                       ^

answered Dec 22, 2013 at 3:41

Mitch Wheat

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