如何使用 c# 检查值是否已存在于数据库中以实现统一（SQL 语法错误）

Question

I'm trying to get if a value already exists in my database for a registration and I've searched everywhere for an answer but I get this error:

" You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near...at line 1".

I don't know what I'm doing wrong...

void Start()
{
    linhaConn = "Server=localhost;" +
        "Database=jogo;" +
        "User ID=root;" +
        "Password=;" +
        "Pooling=false;" +
        "CharSet=utf8";
    ConnDatabase(linhaConn);

}

void ConnDatabase(string lConn)
{
    conn = new MySqlConnection(lConn);
    conn.Open();
    
    print("Conectado"); 
}

public void InserirDB()
{   
    ConnDatabase(linhaConn);
    txtUser = InpUserCriar.text;
    txtEmail = InpEmail.text;

    command = new MySqlCommand("select * from jogador where ([email] = '" + txtEmail + "')", conn);
    int UserExist = (int)command.ExecuteScalar();

    if (UserExist > 0)
    {
        print("already exists");
    }
    else
    {
        print("doesnt exists");
    }

    conn.Close();

EDIT I did it: Here is the code:

   ConnDatabase(linhaConn);
    txtUser = InpUserCriar.text;
    txtEmail = InpEmail.text;

    string countDataEmail;
    command = new MySqlCommand("select count(*) from jogador where email= '" + txtEmail+ "' ;", conn);
    countDataEmail = command.ExecuteScalar().ToString();
    if (countDataEmail == "0")
    {
        print("it doesnt exist");
    }
    else
    {
        print("email already exists");
    }

Answer 1

If you just want to check if they query returns ant row you can use UserExist.HasRows

Answer 2

I just wanted to mention SQL Injection . Whenever dealing with User Input make sure they can't harm or retrieve something from your database. See the example which uses a prepared statement to avoid that.

---

besides that, are you sure it should be

... where ([email] = some@email.address)

instead of (how I know SQL queries)

... where email = some@email.adddres;

---

So together it would probably be something like

command = new MySqlCommand("select * from jogador where email = @email;", conn);
command.Parameters.AddWithValue("@email", txtEmail);
commandPrepare();