Use the results of an SQL query to create another query

Question

I am working on a bidding/allocation system using C# and MySQL, and I am currently having difficulty implementing the “post-allocation” mechanics of the system. Let me explain how it works, before introducing the code:
When the bids are made on the system, they all have the position 0, so the first thing the system does is order them according to priority.
 (bid table)
In this case, 5 bidders are interested in what is in plot 15, but we have not assigned them a position yet.
 (bid table)
The system then organises the bids according to the order in which they are going to processed.
The bids are then allocated, but unfortunately there are only 3 spaces in plot 15 that can be allocated. As a result, we use the priority listing to determine which bidder gets what.
 (booking table)
At this stage, I can say that I am stuck, there are two things that I want to do, both of which involve reusing the results of the query at step 2.
 (bid table)
The bidders that have their job allocated should see: their bid.status updated
from Queued to Allocated,
the bid.position should
be set to 0,
and their job_id should
be set to the booking they have been allocated (i.e. booking.id).
The bidders that have not had their jobs allocated should see: their bid.status remain
as Queued, and their bid.position should
be set to 0 in
preparation for the method to run again
The difficulty I am having is in stage 3, how do I determine which jobs have been allocated and which ones have not, and then run the necessary SQL queries in order to make the updates?
My code so far is as follows:
// STEP 1a - SELECT BIDS
string query =
"SELECT t1.operator_id, t1.datetime, t1.plot_id, t1.position, t2.market_access FROM bid t1 " +
"JOIN operator t2 ON t1.operator_id = t2.id WHERE t1.status='Queued' AND t1.postcode=@postcode " +
"ORDER BY t2.market_access ASC, t1.datetime ASC";
var bidList = new List<BidList>();
var cmd = new MySqlCommand(query, _connection);
cmd.Parameters.AddWithValue(("@postcode"), _plot);
MySqlDataReader dataReader = cmd.ExecuteReader();
while (dataReader.Read())
var item = new BidList
OperatorId = dataReader["operator_id"] + "",
PlotId = dataReader["plot_id"] + "",
Position = dataReader["position"] + "",
Datetime = dataReader["datetime"] + "",
MarketAccess = dataReader["market_access"] + "",
bidList.Add(item);
dataReader.Close();
// STEP 1b - SET PRIORITIES
for (var i = 0; i < bidList.Count; i++)
var position = i + 1;
bidList[i].Position = position.ToString();
query = "UPDATE bid SET position=@position WHERE status='Queued' AND postcode=@postcode AND operator_id=@operator_id;";
cmd = new MySqlCommand(query, _connection);
cmd.Parameters.AddWithValue(("@position"), position);
cmd.Parameters.AddWithValue(("@postcode"), _plot);
cmd.Parameters.AddWithValue(("@operator_id"), bidList[i].OperatorId);
cmd.ExecuteNonQuery();
dataReader.Close();
// STEP 2 - ALLOCATE JOBS ACCORDING TO PRIORITY
foreach (var t in bidList)
query = "SELECT operator_id, plot_id, status FROM booking " +
"WHERE status='open' AND postcode=@postcode AND operator_id='0'" +
"ORDER BY datetime ASC;" +
"UPDATE booking SET operator_id=@operator_id, status='Allocated' " +
"WHERE (plot_id=@plot_id AND operator_id='0' AND status='Open') LIMIT 1;";
cmd = new MySqlCommand(query, _connection);
cmd.Parameters.AddWithValue(("@operator_id"), t.OperatorId);
cmd.Parameters.AddWithValue(("@postcode"), _plot);
cmd.Parameters.AddWithValue(("@plot_id"), t.PlotId);
cmd.ExecuteNonQuery();
dataReader.Close();
// STEP 3
CloseConnection();

Answer 1

I can't tell.  When modifying row(s) you have to be able to uniquely be able to identify the row(s) in the database you want to modify.  That is why I recommended the other day to use DataAdapter instead of the DataReader.  You can with the
reader, but you need to unique identify the rows.
I can't tell from the limited amount of data you posted if in table 2 that there is only one row with the same operator id and plot id.  It looks like in table 2 the 'id' number is unique.  When working with a database with multiple tables you
need to be able to link tables together with primary keys (columns wit unique values).  If the database isn't designed properly then it is impossible to do some operations.  So you always have to make sure you design a database properly.
jdweng
When you say table 2 are you referring to the bid or booking table?
Here is the table structure for the bid table
Here is the table structure for the booking table
Hope it helps makes things clearer!