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Discussion of article "How to Access the MySQL Database from MQL5 (MQL4)"

MetaQuotes · 2025-01-15T21:01:53.0000000Z

New article How to Access the MySQL Database from MQL5 (MQL4) has been published: The article describes the development of an interface between MQL and the MySQL database. It discusses existing practical solutions and offers a more convenient way to implement a library for working with databases. The article contains a detailed description of the functions, the interface structure, examples and some of specific features of working with MySQL. As for the software solutions, the article attachments include the files of dynamic libraries, documentation and script examples for the MQL4 and MQL5 languages. The problem of interaction of MQL with databases is not new, however it's still relevant. Use of databases can greatly enhance the possibilities of MetaTrader: storage and analysis of the price history, copying trades from one trading platform to another, providing quotes/trades in real time, heavy analytical computations on the server side and/or using a schedule, monitoring and remote control of accounts using web technologies. Anyway, there were many attempts to benefit from the combination of MQL and MySQL, some solutions are available in the CodeBase. For example "MySQL wrapper - library for MetaTrader 4" is the project, from which many programmers start their own developments with further additions. In my opinion, one of the disadvantages of this solution is allocation of special arrays for reading data from the database. Another project "MySQL logger 1 - EA for MetaTrader 4" is highly specialized, it uses no wrapper to access the standard library libmysql.dll. Therefore it doesn't work in MetaTrader4 Build 600+, since the char character types have been replaced by wchar_t , and the use of the int type instead of the TMYSQL structure pointer causes memory leaks in the project (the allocated memory cannot be controlled/freed). Another interesting project is "EAX_Mysql - MySQL library - library for MetaTrader 5" . It's quite a good implementation. The list of disadvantages stated by the author imposes some restrictions on its use. Anyone who ever needs to uses databases in their MQL projects has two options: either to develop their own solution and know every single part of it, or use/adapt any third-party solution, learn how to use it and detect all its defects that may hinder their project. I faced such a necessity and the two options while developing a rather complex trading robot. Having searched through existing projects and studied a very large number of solutions, I realized that non of the found implementations could help bring my trading robot to the "professional level". Moreover, there were also absurd solutions, for example: DML/DDL operations (insert/update/delete data, create/drop objects in database) were performed using the standard libmysql.dll, and data selection (SELECT) was actually implemented as a HTTP request (using inet.dll) to a PHP script located on the web server on the MySQL server side. The SQL queries were written in the PHP script. In other words, to run the project, one needed to keep the following components available, configured and running: MySQL server, Apache/IIS web server, PHP/ASP scripts on the server side... A combination of quite a large number of technologies. Of course, in some circumstances this may be acceptable, but when the only task is to select data from the database - this is nonsense. In addition, supporting such a cumbersome solution is time-consuming. Most of the solutions had no problems inserting data, creating objects and the like. The problem was data selection, as the data should be returned to the calling environment. I thought using arrays for this purpose was impractical and inconvenient, simply because in the course of development/debugging/support of the main project, select queries to the database can be changed, while you should also control correct memory allocation for the arrays... Well, this can and must be avoided. The hereinafter discussed MQL <-> MySql interfaced is based on a typical approach used in Oracle PL/SQL, MS SQL T-SQL, AdoDB - use of cursors. This interface was developed targeting the ease of programming and maintenance, plus a minimum of components. It is implemented as a DLL wrapper to the standard library libmysql.dll and a set of interface functions as an .mqh file. 1. MQL <-> MySQL Interface The interaction between the MetaTrader terminal (through MQL programs) can be implemented with the help of the below components: Author: Eugeniy Lugovoy

Eugeniy Lugovoy 2016.10.18 09:06 #121

Pavel Kolchin:

win 7 x64 - mt5 x64 latest version (v5 b1455)

I can't get to MySQL, but it's not a pity.

Server: Localhost via UNIX socket

Server type: Percona Server

Server Version: 5.5.35-33.0-log - Percona Server (GPL), Release rel33.0, Revision 611

Protocol Version: 10

User: ***

Server encoding: UTF-8 Unicode (utf8)

works in mql4

The error has been reproduced. I will solve it...

Eugeniy Lugovoy 2016.10.18 12:53 #122

Here is the recompiled x64 for MQL5

Pavel try it.

Files:

MQL5_x64.zip 1412 kb

Pavel Kolchin 2016.10.18 13:59 #123

Eugeniy Lugovoy:

no more problems with dll's connection

everything works, thanks

Eugeniy Lugovoy 2016.10.18 16:43 #124

Pavel Kolchin:

no more problems with dll's connection

everything works, thanks

Always happy to help.

Good luck with your projects.

--- 2016.10.18 19:14 #125

Yuriy Asaulenko:

Thanks, I read it. There's a very good point there by the author of the current article, who came in,..... and ruined everything.)

I myself have encountered more than once the problem of collisions on it. For example, if a trading robot is attached to different charts, but uses one base, and the access is to one general-purpose table (say registration/change of sessions, accounts), then in any case you will get an error like "table locked". And it doesn't matter that all transactions are completed, cursors are closed and the database was opened in shared mode.

The commentator probably did not understand the sqlite settings, which resolve all collisions through compilation for mode with locks or through pragma.

I can say that I have been working for several years on heavy projects with simultaneous read/write multithreading and there are no problems, the main thing is to have straight hands.

Errors, bugs, questions Failure to fulfil their Experiment

Eugeniy Lugovoy 2016.10.18 20:44 #126

o_O:

The commenter probably did not understand the sqlite settings, which resolve all collisions through compilation for mode with locks or through pragma.

I can say that I have been working for several years on heavy projects with simultaneous read/write multithreading and there are no problems, the main thing is to have straight hands.

o_O

If anything I can pick up that project for SQLite, write test scripts/EA and if there will be locks again, we can figure it out together (if you don't mind) and provide a software solution to the community.

It might be worth paying attention to this as there are some advantages of a DB (autonomy, SQL, mobility, embeddability, etc).

In fact, I took a ready DLL from SQLite (not the source code) and did not recompile it, but just worked with C++ API.

Output test results to Making a Python trading Engineer Garin's Paraboloid

Yuriy Asaulenko 2016.10.18 21:54 #127

Eugeniy Lugovoy:

o_O

If anything I can pick up that project for SQLite, write test scripts/EA and if there are locks again, we can figure it out together (if you don't mind) and provide a software solution to the community.

It might be worth paying attention to this as there are some advantages of a DB (autonomy, SQL, mobility, embeddability, etc).

In fact, I took a ready-made DLL from SQLite (not the source code) and didn't recompile it, just worked with the C++ API.

It would be really interesting if the "myth" of SQLite locking was confirmed or dispelled. If it weren't for this uncertainty, or solutions to address it, SQlite is a very attractive option for interoperability. It would be interesting to know also something about its performance, for example, compared to the same database with Access. Of course, if someone has a real time and desire to do such work.

There are still questions of connecting the base to third-party software, which can be connected to any database - Access, SQL Server, Oracle and so on. Does SQLite has a driver installed on the computer like OLEDB or at least ODBC? And in the same Access several applications can write-read to the same database asynchronously through different interfaces without any problems. I suspect that this may not work with SQLite.

Without open interest it's Suggestions on making acess Libraries: AdoSuite v 1.0

Eugeniy Lugovoy 2016.10.18 22:57 #128

Yuriy Asaulenko:

It would be really interesting if the "myth" of SQLite locking was confirmed or dispelled. If not for this uncertainty, or solutions to eliminate it, SQlite is a very attractive option for interoperability. It would be interesting to know also something about its performance, for example, compared to the same database with Access. Of course, if someone has a real time and desire to do such work.

There are still questions of connecting the base to third-party software, which can be connected to any database - Access, SQL Server, Oracle and so on. Does SQLite has a driver installed on the computer like OLEDB or at least ODBC? And in the same Access several applications can write-read to the same database asynchronously through different interfaces without any problems. I suspect that this may not work with SQLite.

Well OLEDB for SQLite is available, just google it. By the way, an interesting idea to run test scripts about locating through OLEDB to SQLite.... perverted, of course, but we are all perverts here....

And on the native access, I believe that by joint efforts we can achieve a positive result. It's just a matter of time, I won't be able to do it this week... maybe at the weekend I'll make some time...

An idea for a Features of the mql5 Raw Ideas

Yuriy Asaulenko 2016.10.19 01:40 #129

Eugeniy Lugovoy:

Well OLEDB for SQLite is available, just google it. By the way, interesting idea to run test scripts about loc via OLEDB to SQLite.... perverted of course, but we are all perverts here....

And on the native access, I believe that by joint efforts we can achieve a positive result. It's just a matter of time, I won't be able to do it this week... maybe on the weekend I will allocate time...

I have an application that creates a database and writes (not read) into it large amounts of information in many tables. If I can find an OLEDB driver that is installed on the computer and visible through the application settings, SQLite can be easily tested for no hangs. Similarly, you can connect to SQLite the same Access and try to read and modify tables in parallel. Something to measure, of course, will not be possible.

Looked through the internet. At once such OLEDB provider could not find such an OLEDB provider. All more OLEDB DLLs, which can be used only from programming languages, as far as I understand.

Errors, bugs, questions Without open interest it's Writing to the file

Pavel Kolchin 2016.10.20 14:11 #130

started popping up all the time, what does that mean?

When I run my code on this line.

if(DB==-1){DB=MySqlConnect(Host, User, Password, Database, Port, Socket, ClientFlag);}

res = MySqlCursorOpen(DB, "SELECT id, account, symbol FROM `current` WHERE account="+account);

Connecting to a MySql Can MQL use Database Help how to connect

Discussion of article "How to Access the MySQL Database from MQL5 (MQL4)" - page 13