I am developing a cricket simulation and i need to retrieve certain statistics from a players data. I've got the following code.
public List<float> BattingData()
{
con.ConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString.ToString();
string query = "SELECT [INNS], [NOT OUTS], [AVG] FROM [" + batTeam + "] WHERE [Player] = '" + name + "';";
SqlCommand com = new SqlCommand(query, con);
con.Open();
using (SqlDataReader reader = com.ExecuteReader())
{
if(reader.HasRows)
{
while (reader.NextResult())
{
Innings = Convert.ToInt32(reader["INNS"]);
NotOuts = Convert.ToInt32(reader["NOT OUTS"]);
Avg = Convert.ToSingle(reader["AVG"]);
}
}
}
con.Close();
OutRatePG = (Innings = NotOuts) / Innings;
OutRatePB = OutRatePG / 240;
RunsPB = Avg / 240;
battingData.Add(OutRatePB);
battingData.Add(RunsPB);
return battingData;
}
The error that I am getting is that when I try to divie by 'Innings' it is saying cannot divide by zero, so I think the variables are being returned as zero and no data is being assigned to them.
This line is the issue:
while (reader.NextResult())
What this does is move the reader to the next resultset, ignoring the rest of the rows unread. To advance a reader to the next row, you need to call reader.Read() instead.
You have some other issues with your code:
You appear to have a separate table for each team. This is incorrect database design. You should create a Team table, with each team in it, and then foreign key your TeamResults table to it. Query it using INNER JOIN.
You are concatenating user-entered values to your query. This leaves you open to SQL injection attacks. Use parameters instead. (You cannot parameterize a table name, another reason you should do as above 1.)
You do not need to check for HasRows. If there are no rows, Read() will return false.
It looks like you only want one row. If that is the case you don't want a while(reader.Read()) loop, instead if(reader.Read()). (If you only need a single value, you can refactor the code to use command.ExecuteScalar().)
In database records check if value for Innings has 0
also you can try the below code before performing any operation.
> if(Innings>0) { OutRatePG = (Innings - NotOuts) / Innings; }
Related
How to display the unitfunction value from mysql database and my query is below ,i don't know its right or wrong.
Help me out.
string fundev = "select unitfunctioncode from channels where channel_no = " + Channelid;
MySqlCommand getfun = new MySqlCommand(fundev, Connection1);
Console.WriteLine(getfun);
MAKE ENTITY CONTEXT FIRST:
YourEntity db= new YourEntity();
LINQ:
Console.Write(db.channels.Where(x=>x.channel_no == Channelid).Select(y=>y.unitfunctioncode));
This is modal first approach create modal from database and call this linq in controller
I'm not sure about the specifics of MySqlCommand, but I would expect to see an execute on your getfun object.
I would do something like this:
MySqlDataReader rdr = getfun.ExecuteReader();
while (rdr.Read())
{
Console.WriteLine(rdr[0]);
}
rdr.Close();
This takes into account multiple rows returned. You can omit the while loop if you're sure you will have a single row returned.
I am making something that requires MySQL. I have the saving done from in-game, which is simply done by INSERT.
I have a column that will have a password in and I need to check if the inputted password matched any of the rows and then if it is, get all of the contents of the row then save it to variables.
Does anyone have an idea how to do this in C#?
//////////////////////////
I have found how to save and get the string, however it will only get 1 string at a time :(
MySql.Data.MySqlClient.MySqlCommand command = conn.CreateCommand();
command.CommandText = "SELECT * FROM (player) WHERE (pass)";
command.ExecuteNonQuery();
command.CommandType = System.Data.CommandType.Text;
MySql.Data.MySqlClient.MySqlDataReader reader = command.ExecuteReader();
reader.Read();
ayy = reader.GetString(1);
print (ayy);
if(ayy == password){
//something
}
My best practice is to use MySQLDataAdapter to fill a DataTable. You can then iterate through the rows and try to match the password.
Something like this;
DataTable dt = new DataTable();
using(MySQLDataAdapter adapter = new MySQLDataAdaper(query, connection))
{
adapter.Fill(dt);
}
foreach(DataRow row in dt.Rows)
{
//Supposing you stored your password in a stringfield in your database
if((row.Field<String>("columnName").Equals("password"))
{
//Do something with it
}
}
I hope this compiles since I typed this from my phone. You can find a nice explanation and example here.
However, if you are needing data from a specific user, why not specificly ask it from the database? Your query would be like;
SELECT * FROM usercolumn WHERE user_id = input_id AND pass = input_pass
Since I suppose every user is unique, you will now get the data from the specific user, meaning you should not have to check for passwords anymore.
For the SQL statement, you should be able to search your database as follows and get only the entry you need back from it.
"SELECT * FROM table_name WHERE column_name LIKE input_string"
If input_string contains any of the special characters for SQL string comparison (% and _, I believe) you'll just have to escape them which can be done quite simply with regex. As I said in the comments, it's been a while since I've done SQL, but there's plenty of resources online for perfecting that query.
This should then return the entire row, and if I'm thinking correctly you should be able to then put the entire row into an array of objects all at once, or simply read them string by string and convert to values as needed using one of the Convert methods, as found here: http://msdn.microsoft.com/en-us/library/system.convert(v=vs.110).aspx
Edit as per Prix's comment: Data entered into the MySQL table should not need conversion.
Example to get an integer:
string x = [...];
[...]
var y = Convert.ToInt32(x);
If you're able to get them into object arrays, that works as well.
object[] obj = [...];
[...]
var x0 = Convert.To[...](obj[0]);
var x1 = Convert.To[...](obj[1]);
Etcetera.
I have a datatable that may have 1000 or so rows in it. I need to go thru the datatable row by row, get the value of a column, run a query (Access 2007 DB) and update the datatable with the result. Here's what I have so far, which works:
String FilePath = "c:\\MyDB.accdb";
string QueryString = "SELECT MDDB.NDC, MDDB.NDC_DESC "
+ "FROM MDDB_MASTER AS MDDB WHERE MDDB.NDC = #NDC";
OleDbConnection strAccessConn = new OleDbConnection(string.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + FilePath));
strAccessConn.Open();
OleDbDataReader reader = null;
int rowcount = InputTable.Rows.Count; //InputTable is the datatable
int count = 0;
while (count < rowcount)
{
string NDC = InputTable.Rows[count]["NDC"].ToString();
//NDC is a column in InputTable
OleDbCommand cmd = new OleDbCommand(QueryString, strAccessConn);
cmd.Parameters.Add("#NDC", OleDbType.VarChar).Value = NDC;
reader = cmd.ExecuteReader();
while (reader.Read())
{
//update the NDCDESC column with the query result
//the query should only return 1 line
dataSet1.Tables["InputTable"].Rows[count]["NDCDESC"] = reader.GetValue(1).ToString();
}
dataGridView1.Refresh();
count++;
}
strAccessConn.Close();
However this seems very inefficient since the query needs to run one time for each row in the datatable. Is there a better way?
You're thinking of an update query. You don't actually have to go over every row one by one. SQL is a set based language, so you only have to write a single statement that it should do for all rows.
Do this:
1) Create > Query Design
2) Close the dialog that selects tables
3) Make sure you're in sql mode (top left corner)
4) Paste this:
UPDATE INPUTTABLE
INNER JOIN MDDB_MASTER ON INPUTTABLE.NDC = MDDB_MASTER.NDC
SET INPUTTABLE.NDCDESC = [MDDB_MASTER].[NDC_DESC];
5) Switch to design mode to see what happens. You may have to correct Input table, I couldn't find it's name. I'm assuming they;re both in the same database.
You'll see the query type is now an update query.
You can run this text through cmd.ExecuteNonQuery(sql) and the whole thing should run very quickly. If it doesn't you'll need an index on one of the tables;
THis works by joining the two table on NDC and then copying the NDC_DESC over from MDDB_MASTER to the inputtable.
I missed the part about InputTable coming from Excel.
For better speed, instead of executing the query in Access over and over, you can get all rows from MDDB_MASTER into a datatable in one select statement:
SELECT MDDB.NDC, MDDB.NDC_DESC FROM MDDB_MASTER
And then use the DataTable.Select method to filter the right row.
mddb_master.Select("NDC = '" + NDC +'")
This will be done in memory and should be much faster than all the round trips you have now. Especially over the network these round trips are expensive. 225k rows should be only a few MB (roughly a JPEG image) so that shouldn't be an issue.
You could use the "IN" clause to build a bigger query such as:
string QueryString = "SELECT MDDB.NDC, MDDB.NDC_DESC "
+ "FROM MDDB_MASTER AS MDDB WHERE MDDB.NDC IN (";
int rowcount = InputTable.Rows.Count; //InputTable is the datatable
int count = 0;
while (count < rowcount)
{
string NDC = InputTable.Rows[count]["NDC"].ToString();
QueryString += (count == 0 ? "" : ",") + "'" + NDC + "'";
}
QueryString += ")";
You can optimize that with StringBuilders since that could be a lot of strings but that's a job for you. :)
Then in a single query, you would get all the NDC descriptions you need and avoid performing 1000 queries. You would then roll through the reader, find values in the InputTable, and update them. Of course, in this case, you're looping through the InputTable multiple times but it might be a better option. Especially if yor InputTable could hold duplicate NDC values.
Also, note that you have a OleDbDataReader leak in your code. You keep reassigning the reader reference to a new instance of a reader before disposing of the old reader. Same with commands. You keep instantiating a new command but are not disposing of it properly.
My C# code below checks a SQL database to see if a record matches a ClientID and a User Name. If more than 15 or more matching records are found that match, the CPU on my Windows 2008 server peaks at about 78% while the 15 records are found while the below C# code executes. The SQL Server 2008 database and software is located on another server so the problem is not with SQL Server spiking the CPU. The problem is with my C# software that is executing the code below. I can see my software executable that contains the C# code below spike to 78% while the database query is executed and the records are found.
Can someone please tell me if there is something wrong with my code that is causing the CPU to spike when 15 or more matching records are found? Can you also please tell/show me how to optimize my code?
Update: If it finds 10 records, the CPU only spikes at 2-3 percent. It is only when it finds 15 or more records does the CPU spike at 78% for two to three seconds.
//ClientID[0] will contain a ClientID of 10 characters
//output[0] will contain a User Name
char[] trimChars = { ' ' };
using (var connection = new SqlConnection(string.Format(GlobalClass.SQLConnectionString, "History")))
{
connection.Open();
using (var command = new SqlCommand())
{
command.CommandText = string.Format(#"SELECT Count(*) FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'");
command.Connection = connection;
var rows = (int) command.ExecuteScalar();
if (rows >= 0)
{
command.CommandText = string.Format(#"SELECT * FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'");
using (SqlDataReader reader = command.ExecuteReader())
{
if (reader.HasRows)
{
while (reader.Read())
{
//Make sure ClientID does NOT exist in the ClientID field
if (reader["ClientID"].ToString().TrimEnd(trimChars).IndexOf(ClientID[0]) !=
-1)
{
//If we are here, then do something
}
}
}
reader.Close();
reader.Dispose();
}
}
// Close the connection
if (connection != null)
{
connection.Close();
}
}
}
You can decrease the number of database access from 2 to 1 if will remove first query, it is not necessary.
using (SqlConnection connection = new SqlConnection(connectionString))
using (SqlCommand command = connection.CreateCommand())
{
command.CommandText = "SELECT ClientID FROM dbo.Filelist WHERE ToAccountName = #param"; // note single column in select clause
command.Parameters.AddWithValue("#param", output[0]); // note parameterized query
connection.Open();
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read()) // reader.HasRow is doubtfully necessary
{
// logic goes here
// but it's better to perform it on data layer too
// or return all clients first, then perform client-side logic
yield return reader.GetString(0);
}
} // note that using block calls Dispose()/Close() automatically
}
Change this:
SELECT * FROM Filelist
To this:
SELECT ClientID FROM Filelist
And check for performance.
I suspect there is a blob field on your select.
Also select * is not recommended, write your exact interested fields in your query.
Nothing looks obviously CPU intensive, but one problem does stand out.
You are running a query to count how many records there are
"SELECT Count(*) FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'"
Then, if more than 0 is returned, you are running another query to get the data.
"SELECT * FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'"
This is redundant. Get rid of the first query, and just use the second one, checking to see if the reader has data. You can also get rid of the HasRows call and just do
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
}
}
Please consider what already said about parametrized queries.
Beside that, I think that the only big issue could arise in the following block:
while (reader.Read())
{
//Make sure ClientID does NOT exist in the ClientID field
if (reader["ClientID"].ToString().TrimEnd(trimChars).IndexOf(ClientID[0]) != -1)
{
//If we are here, then do something
}
}
So try to just cache your reader.Read() data in some local variable, releasing the SQL resources asap, then you can work on the data you just retrieved. Eg:
List<string> myRows = new List<string>();
while (reader.Read())
{
myRows.Add(reader["ClientID"].ToString();
}
/// quit the using clause
/// now elaborate what you got in myRows
There is nothing in the code to indicate a performance problem.
What does SQL Profiler show?
(Both in terms of query plan, and server resources used.)
Edit: To make this clearer: you have one measurement that might indicate an issue. You now need to measure more deeply to understand if it really is a problem, only you can do this (no one else has access to the hardware).
I strongly recommend that you get a copy of dotTrace from JetBrains.
At the very least, profiling the client code will help you identify/eliminate the source of the CPU spike.
I recommend using parameters as suggested, however, I have seen performance problems where the type of the string column does not match the C# string. In these cases, I suggest specifying the type explicitly.
Like this:
command.CommandText = "SELECT ClientID FROM dbo.Filelist WHERE ToAccountName = #accountName";
command.Parameters.Add("#accountName", SqlDbType.NVarChar, 16, output[0]);
Or this:
SqlParameter param = command.Parameters.Add(
"#accountName", SqlDbType.NVarChar);
param.Size = 16; //optional
param.Value = output[0];
I have this SQL Table:
TABLE: Info
COLUMNS:| Name | Value
--------|----------|------------------
ROW: | Server | 255.255.255.255
ROW: | Host | 212.212.212.212
ROW: | User | Admin
I'm selecting this table like that: SELECT * FROM Info
Now after I got all in this table.
I want to get the value Where Name = 'Server' and put it into the Server variable.
What is the best method to do it in C#?
DataSet? DataReader? And how can I accomplish this?
If you didn't understand what I need here is another good explanation thx to Tim:
I'm trying to get a specified column's value based on the value in another column of the same row
Based on your latest comments, it appears that you want to get all the rows in the table, and then be able to select a given row based on the Name column.
A DataTable would be best if your program is going to need to access the different rows at different times - as long as the DataTable is in memory/cached, you can pull the value for any name at any time.
If you just need to do it once, a SqlDataReader would probably be faster, but its forward-only.
DataTable example:
Assuming you've already filled the DataTable (name info in the example), you can use the Select method:
DataRow[] selectedRows = info.Select("Name = 'Server'");
string serverIP = selectedRows[0]["Value"].ToString();
DateReader example:
Based upon #Kobe's code, simply check the Name each time you advance to the next record, and then pull the Value out:
bool valueFound = false;
while (reader.Read() && !valueFound)
{
if (reader["Name"].ToString() == "Server")
{
serverIP = reader["Value"].ToString();
valueFound = true;
}
}
There are some caveats to be aware of. First, the Select method of the DataTable returns an array of DataRow, so if more than one record has "Server" in the Name column, you'll get multiple results. If that's by design, that's fine - just loop through the array of DataRows.
Second, if there are a lot of rows in the table, or there is the potential down the road, the reader may be slower depending on where the record of interest is in the table. And if you're dealing with the possibility of multiple records in the table matching the Name criteria, it's probably easier all around to just stick with a DataTable.
Is this what you are looking for , if so let me know , i will refine the code with USING key word and remove the sql inline and post you one more answer soon
one more example from google ,
// instantiate and open connection
conn = new
SqlConnection("Server=(local);DataBase=Northwind;Integrated Security=SSPI");
conn.Open();
// don't ever do this!
// SqlCommand cmd = new SqlCommand(
// "select * from Customers where city = '" + inputCity + "'";
// 1. declare command object with parameter
SqlCommand cmd = new SqlCommand(
"select * from Customers where city = #City", conn);
// 2. define parameters used in command object
SqlParameter param = new SqlParameter();
param.ParameterName = "#City";
param.Value = inputCity;
// 3. add new parameter to command object
cmd.Parameters.Add(param);
// get data stream
reader = cmd.ExecuteReader();
// write each record
while(reader.Read())
{
Console.WriteLine("{0}, {1}",
reader["CompanyName"],
reader["ContactName"]);
}
}
finally
{
// close reader
if (reader != null)
{
reader.Close();
}
// close connection
if (conn != null)
{
conn.Close();
}
}
other example...
SqlCommand sqlComm = new SqlCommand("SELECT * FROM Info where name='+server+'", sqlConn);
SqlDataReader r = sqlComm.ExecuteReader();
while ( r.Read() ) {
string name = (string)r["Name"];
Debug.WriteLine(username + "(" + userID + ")");
}
r.Close();