Support for old versions of mysql

[gingermusketeer]

Hi,

I am just starting using rust and I am using this library to connect to an old version of mysql. The version is 5.0.37. With more recent versions such as 5.6 this library works great. However when trying to connect to the older version 5.0.37 I get the following error:

Error: error returned from database: 1064 (42000): You have an error in your SQL
 syntax; check the manual that corresponds to your MySQL server version for the
right syntax to use near ';
            SET time_zone = '+00:00'' at line 1

Running the commands one by one from

sqlx/sqlx-core/src/mysql/connection/mod.rs

Lines 128 to 130 in f85920a

	SET sql_mode=(SELECT CONCAT(@@sql_mode, ',PIPES_AS_CONCAT,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE'));
	SET time_zone = '+00:00';
	SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci;

I discovered that SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci; does not work because utf8mb4 was added in mysql 5.3.

Removing this line I also discovered that the other lines do not work as they are now. It appears that mysql does not support multiple statements in the same call to execute.

Is this something that sqlx could support? Completely understand if this is not something you want to support given the age of the database.

[mehcode]

Does #425 fix your issue?

I don't mind tweaking things to support older clients. I don't want to chase bugs in them but I'll definitely merge support. MySQL has this excellent system called capabilities where it tells us what it can do so we could adapt to even older servers.

[gingermusketeer]

@mehcode I tested the version of mysql that I am using and it does support multiple configuration options in the SET command like that done in #425. However there is still the issue with utf8mb4 not being supported.

What would be the best way do disable that part of the connection setup in your opinion? I could have a go a making the change once #425 is merged.

[mehcode]

@gingermusketeer How about storing the server_version received from the Handshake and checking that. If it's below 5.3 you can use utf8 instead of utf8mb4. It's still important that we tell MySQL we're using UTF-8.

[mehcode]

@gingermusketeer master should have support for MySQL 5.0 now. The tests don't pass because the tests assume a connection that can do multiple statements. But the tests that matter pass and it should work.