Check if record in a table exist in a database through ExecuteNonQuery

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If you want to check if the user exists, you have to change your sql and use COUNT or EXISTS:

So instead of 

SELECT * from users where user_name like 'Adam' AND password like '123456'

this

SELECT COUNT(*) from users where user_name like 'Adam' AND password like '123456'

Now you can use ExecuteScalar to retrieve the count of users with this username and password:

int userCount = (int) sqlCommand.ExecuteScalar();
if(userCount > 0)
    // user exists ....

Note that you should use sql-parameters to prevent sql-injection:

using (SqlCommand sqlCommand = new SqlCommand("SELECT COUNT(*) from users where user_name like @username AND password like @password", sqlConnection))
{
    sqlConnection.Open();
    sqlCommand.Parameters.AddWithValue("@username", userName);
    sqlCommand.Parameters.AddWithValue("@password", passWord);
    int userCount = (int) sqlCommand.ExecuteScalar();
    ...
}

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