How to execute multiple statement with variables in C# OdbcCommand object - mysql

Question

I want to execute below MySql queries at a time through OdbcCommand object within C# as dynamic query, it always fails:
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
set #row=0;
select * from
(
select #row:=#row+1 as my____row_num,
cities.`cityid`,
cities.`cityname`,
cities.`countryid`,
cities.`countryname` , '1' as my____data_row_created , '1' as
my____data_row_updated from `cities` ) p
where my____row_num>=101 and my____row_num<=200;
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ ;
I'm using below method to execute above MySql queries:
ExcuteCommand(Sql)
{
DataTable dt = new DataTable();
OdbcCommand SQLCommand = new OdbcCommand(Sql);
OdbcConnection Con = new OdbcConnection(ConnectionString);
try
{
Con.Open();
SQLCommand.Connection = Con;
OdbcDataAdapter da = new OdbcDataAdapter(SQLCommand);
da.Fill(dt);
Con.Close();
Con.Dispose();
}
catch
{
try
{
Con.Close();
}
catch { }
throw;
}
return dt;
}

Answer 1

I found solution from here. While executing multiple dynamic MySql statements through ODBC in C# we have two options:
Execute separately every command
Use stored procedures
In my case I'm bound to use dynamic-quires because I'm having only read-access on database.
Solution:
Rather than Declaring variable and set it, I used another technique to use a session variable as a derived table and crossed join it with the main table. See the following query, in my scenario I changes to below MySql query code and removed both SET SESSION related code from the query, and it worked properly:
select * from
(
select #row:=#row+1 as my____row_num,
cities.`cityid`,
cities.`cityname`,
cities.`countryid`,
cities.`countryname` , '1' as my____data_row_created , '1' as
my____data_row_updated from `cities` ,(select #row:=0) as t ) p
where my____row_num>=101 and my____row_num<=200;

Answer 2

I'm not going to attempt to solve your MySQL problem, but your C# code can and should be written better, and since comments are not suited for codes, I thought I'd better write this as an answer.
So here is an improvement to your C# part:
DataTable FillDataTable(string sql)
{
var dataTable = new DataTable();
using(var con = new OdbcConnection(ConnectionString))
{
using(var command = new OdbcCommand(sql, con))
{
using(var dataAdapter = new OdbcDataAdapter(SQLCommand))
{
dataAdapter.Fill(dataTable);
}
}
}
return dataTable;
}
Points of interests:
I've renamed your method to a more descriptive name. ExecuteCommand doesn't say anything about what this method does. FillDataTable is self explanatory.
The using statement ensures the disposing of instances implementing the IDisposable interface - And almost all ADO.Net classes are implementing it.
The disposing of an OdbcConnection also close it, so you don't need to explicitly close it yourself.
There is no point of catching exceptions if you are not doing anything with them. The thumb rule is to throw early, catch late. (actually catch as soon as you can do something about it like write to log, show a message to the user, retry etc').
DataAdapters implicitly opens the Connection object, no need to explicitly open it.
Other two improvements you can do are:
Have this method also accepts parameters.
Have this method also accept the CommandType as a parameter (currently, using a stored procedure with this will not work since the default value of CommandType is Text
So, an even better version would be this:
DataTable FillDataTable(string sql, CommandType commandType, params OdbcParameter[] parameters)
{
var dataTable = new DataTable();
using(var con = new OdbcConnection(ConnectionString))
{
using(var command = new OdbcCommand(sql, con))
{
command.CommandType = commandType;
command.Parameters.AddRange(parameters);
using(var dataAdapter = new OdbcDataAdapter(SQLCommand))
{
dataAdapter.Fill(dataTable);
}
}
}
return dataTable;
}
If you want to improve that even further, You can have a look at my GitHub ADONETHelper project - There I have a single private method for Execute, and the methods for filling data tables, filling data sets, execute non query etc' all use this single method.

Answer 3

would you please try this instead
declare #row int
set #row=0;
select * from
(
select SUM(#row,1) as my____row_num,
cities.cityid as CityID,
cities.cityname as CityName,
cities.countryid as CountryID,
cities.countryname as CountryName ,
'1' as my____data_row_created , '1' as my____data_row_updated from cities) //i did not understand the meaning of this
where (my____row_num BETWEEN 100 AND 200 )
backEnd
ExcuteCommand(Sql)
{
<AddThis>ConnectionString= ConfigurationManager.ConnectionStrings["YourDataBaseLocation_OR_theConnectionCreatedViaProperties"].Connectionstring;</AddThis>
DataTable dt = new DataTable();
<deleteThis> OdbcCommand SQLCommand = new OdbcCommand(Sql);</deletethis>
//You Need to add the connection you have used it and Odbc
//Command.CommandType= CommandType.StoredProcedure();
OdbcConnection Con = new OdbcConnection(ConnectionString);
<AddThis>OdbcCommand SqlCommand = new OdbcCommand(Sql,Con);</AddThis>
try
{
Con.Open();
SQLCommand.Connection = Con;
OdbcDataAdapter da = new OdbcDataAdapter(SQLCommand);
da.Fill(dt);
<add this > SQLCommand.ExecuteNonQuery();</Add this>
Con.Close();
<delete> Con.Dispose();</delete>
}
catch
{
try
{
Con.Close();
}
catch (Exception e) { }
throw (e);
}
return dt;
}