Another command that failed using binary protocol using COLLATE.
example :

CREATE TABLE IF NOT EXISTS `tt` (

`test` varchar(500) COLLATE utf8mb4_unicode_ci NOT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

#Text work well

SELECT * FROM `tt` WHERE `test` LIKE 'jj' COLLATE utf8mb4_unicode_ci;

#will throw an error "Erreur SQL (1253) : COLLATION 'utf8mb4_unicode_ci' is not valid for CHARACTER SET 'binary'"

PREPARE stmt FROM 'SELECT * FROM `tt` WHERE `test` LIKE ? COLLATE utf8mb4_unicode_ci'; 

I think we should have a generic fallback that makes all statements prepareable. Like, prepare stores the SQL statement on the server side and execute just completely executes the statement as in the normal protocol.

Statements that return result sets need to use binary protocol.
But luckily all not-yet-prepareable statements don't send results, so it seems.
All statements using this fallback approach don't have to accept prepared parameters.

This should be a fallback approach that automatically applies to all statements that are not natively prepare-able. Even new statements that can be created in the future.

serg XA RECOVER returns a result set.

oops. indeed. that makes it a bit more complex then

But it looks like metadata the same (depend of parameters but the same). so it is not a big problem to return them after prepare IMHO.

That XA looks like do not have such complex data as ALTER/CREATE so easy can be implemented as prepared IMHO...

actually CREATE/ALTER supported in SP, so to implement them we need only to organise "prepare" test somehow...

so maybe it will be simpler to implement (real list of commands shoud be checked)

The following commands is not currently supported in prepared mode:

SQLCOM_LOAD
SQLCOM_LOCK_TABLES
SQLCOM_UNLOCK_TABLES
SQLCOM_CHANGE_DB
SQLCOM_ALTER_DB
SQLCOM_CREATE_FUNCTION
SQLCOM_ALTER_FUNCTION
SQLCOM_DROP_FUNCTION
SQLCOM_CHECK
SQLCOM_SAVEPOINT
SQLCOM_RELEASE_SAVEPOINT
SQLCOM_BEGIN
SQLCOM_PURGE
SQLCOM_PURGE_BEFORE
SQLCOM_HA_OPEN
SQLCOM_HA_CLOSE
SQLCOM_EMPTY_QUERY
SQLCOM_HELP
SQLCOM_CREATE_PROCEDURE
SQLCOM_CREATE_SPFUNCTION
SQLCOM_CALL
SQLCOM_DROP_PROCEDURE
SQLCOM_ALTER_PROCEDURE
SQLCOM_PREPARE
SQLCOM_EXECUTE
SQLCOM_DEALLOCATE_PREPARE
SQLCOM_CREATE_VIEW
SQLCOM_CREATE_TRIGGER
SQLCOM_DROP_TRIGGER
SQLCOM_XA_START
SQLCOM_XA_END
SQLCOM_XA_PREPARE
SQLCOM_XA_COMMIT
SQLCOM_XA_ROLLBACK
SQLCOM_XA_RECOVER
SQLCOM_ALTER_TABLESPACE
SQLCOM_CREATE_SERVER
SQLCOM_DROP_SERVER
SQLCOM_ALTER_SERVER
SQLCOM_CREATE_EVENT
SQLCOM_ALTER_EVENT
SQLCOM_DROP_EVENT
SQLCOM_SIGNAL
SQLCOM_RESIGNAL
SQLCOM_SHOW_RELAYLOG_EVENTS
SQLCOM_GET_DIAGNOSTICS
SQLCOM_EXECUTE_IMMEDIATE
SQLCOM_CREATE_PACKAGE
SQLCOM_DROP_PACKAGE
SQLCOM_CREATE_PACKAGE_BODY
SQLCOM_DROP_PACKAGE_BODY
SQLCOM_BACKUP
SQLCOM_BACKUP_LOCK