Execute SQL from Metatrader
WOW - Thank you! Very Well Put!
MQL and Databases
Does anybody know of a way to connect to a database from MT4? I imagine it would need to be an external DLL as it doesn't look like there is a data access laryer built in to MQL but it shouldn't be that hard to put together. But before I do it, I wondered it here is one out there already somewhere. What I had in mind was a Generic ODBC or OLEDB connection type of thing so it could be used with multiple DBMS's.
MQL & Databases
Hello TraderGeek,
Yes, you will need an external DLL to do this work for you.
If you have no experience with C++, have a look at Powerbasic.
Powerbasic can create DLL files that can be used in MT4 and
it's syntax is easy to understand.
Coder 
do a search on mysql all the information is there. There is no need to create a DLL as they already exist.
Here's a post about connecting to a MS SQL Server DB, and other DBs in that ADO family:
Excellent! Just what I was looking for.
Excellent! Just what I was looking for.
Great, glad that helped.
Juan
PS. Hey, they merged the two threads! Now it looks like I referenced the very same thread I was posting in! Madness! 
How if its just use msado15.dll directly on MQL dude?...
So no more the extended dll in C, maybe it can give more speed for MQL' execution than using 2 dll files... can you give me the sample of database function on msado15.dll?...just to read the record and execute SQL Command.....
As the logic, MQL can use libmysql.dll directly.....
Any more help with this?
I'm trying to connect to a sql express 2005 database. I'm not a c++ programmer. Does anyone know where I can find a working dll that will do this?
connecting to sql server
Hi, I am trying to follow this tutorial on how to connect to sql server.
In the following directory - C:\Program Files\Common Files\System\ADO\ - I have serveral .dll files.
I have the following:
msado15.dll
msadomd.dll
msador15.dll
msadox.dll
There are few others, but these all have 'ado' in the title.
Can someone tell me which one I should use?
Also, can someone give an example of added the connection string.
And also, this example is extremely basic - in fact it seems to be something like a Northwinds example. Does anyone have examples of getting ticks from MT and storing them in MS Sql Server?
Also, has anyone - or is anyone - successfully using MS SQL server with Metatrader? If so, can you please review the above tutorial and maybe provide some additions, or improvements.
many thanks?
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All,
I've seen a couple of threads about using databases in Metatrader, but I havent seen anything specific about connecting to a Microsoft SQL Server. So, I thought I'd put together a quick tutorial of how to do this in case anybody wants to do something similar. This process should work for any data source that can be accessed via ADO/ODBC/OLE DB (SQL, Access, Excel, etc...)
The following code snippets are a little technical, and will require some basic coding knowledge.
For this task, I started with the ExpertSample sample C++ project in your Metatrader folder "experts\samples\DLLSample". I didn't want to start from scratch figuring out the right type of COM library to build, so I simply used this sample project.
Once you've opened up the project (you'll need Visual Studio), you're ready to use SQL in 4 easy steps!
1) Add a reference to the appopriate ADO dlls at the top of your ExpertSample.cpp page, like so:
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" \
no_namespace rename("EOF", "EndOfFile")
[/PHP]
2) Then you're ready to add the ExecuteScalar method to your code. This function will only return one value from SQL. (Metatrader can only receive basic data types).
MT4_EXPFUNC char * __stdcall ExecuteScalar(char *strSQL)
{
HRESULT hr = S_OK;
char tmpChar[255];
try {
// Define string variables.
_bstr_t strCnn(MY_CONNECTION_STRING); //http://www.connectionstrings.com for more info
::CoInitialize(NULL);
_RecordsetPtr pRstAuthors = NULL;
// Call Create instance to instantiate the Record set
hr = pRstAuthors.CreateInstance(__uuidof(Recordset));
if(FAILED(hr))
{
::CoUninitialize();
return "ERROR: Failed creating record set instance";
}
//Open the Record set for getting records from Author table
try {
pRstAuthors->Open(strSQL,strCnn, adOpenStatic, adLockReadOnly,adCmdText);
} catch (_com_error & ce1) {
::CoUninitialize();
return "ERROR: Unable to open SQL Server";
}
try {
pRstAuthors->MoveFirst();
} catch(_com_error) {
::CoUninitialize();
return ""; //empty data
}
//Loop through the Record set
if (!pRstAuthors->EndOfFile)
{
_variant_t tmpvariant;
//Get the first column value
tmpvariant = pRstAuthors->GetFields()->GetItem((long)0)->GetValue();
strcpy(tmpChar,(_bstr_t)tmpvariant);
}
if (pRstAuthors->State == adStateOpen)
pRstAuthors->Close();
pRstAuthors = NULL;
::CoUninitialize();
}
catch(_com_error & ce)
{
//_bstr_t strError = ce.ErrorMessage;
::CoUninitialize();
return "ERROR: Failed to get data.";
}
return tmpChar;
}
[/PHP]
3) Make sure to add you method name in the ExpertSample.def so that you can call it via Metatrader.
[PHP]
EXPORTS GetIntValue
GetDoubleValue
GetStringValue
GetArrayItemValue
SetArrayItemValue
GetRatesItemValue
SortStringArray
ProcessStringArray
ExecuteScalar
4) Once you add your compiled DLL to the "experts\libraries" folder, you can call your DLL method by adding the following to the top of your MQ4 file:
[PHP]
#import "ExpertSample.dll"
string ExecuteScalar(string strSQL);
#import
That's it! You're ready to start making database calls straight from Metatrader. I'm using this right now to play around with some SELECT/INSERT statements into my SQL Server, trying to play around with some advanced ordering logic.
My next goal: using Sockets from Metatrader to communicate to an external application, preferrably written in C#.
Juan