Based on current own work with proxy tables and Adam's series of questions, I'd like to check my understanding of the way remote data access does work.

Are the following four assumptions correct?

1. Each statement run against a proxy table must be a valid SQL statement for the local SQL Anywhere database server; each referenced column, procedure or function must exist in the current database.

2. The server capabilities are responsible what part of a SQL statement can be sent to the remote server or has to be processed locally; i.e. they have influence whether full or partial passthrough mode can be used.

3. Except the mentioned splitting into partial statements, there is no "rewriting" of statements to make them compatible with the remote server, i.e. if a remote server does support a particular SQL feature but does use a different syntax (or a different name for a semantically equal feature) then the remode data access layer won't rewrite the statement to be sent to the remote server with that syntax. (As a consequence, one won't be able to use such a feature.)

4. In contrast, when using FORWARD TO, the statement has only to be compatible and valid for the remote server.

Question:

Are these assumptions correct?

Some samples used:

I created a readonly MS SQL 2000 remote server (named MS_SVR) and tested with ASA 8.0.3 and SA 11.0.1 and the MS SQL system table sysobjects (as proxy table named MS_sysobjects).

Running the following statement in FORWARD TO mode succeeds both with ASA 8 and SA 11 as the syntax is valid on MS SQL:

forward to MS_SVR { select name, unicode(name) from sysobjects }

Running the same statement

select name, unicode(name) from MS_SysObjects

against the ASA 8.0.3 proxy table fails, as unicode is not a known ASA 8 function. However, running against SA 11.0.1 succeeds as that does support the unicode function. Note, however, that there's no capability for such a function, and therefore the statement is not processed in full passthrough mode:

The query is being processed in NO PASSTHRU mode
The capability check of Unknown builtin function failed
The Remote Statement for vt_1 is 
    select MS_SysObjects.name from MS_SysObjects

An example for the "rewriting" mentioned in Assumption 3 would be the syntax differences between "SELECT TOP" in SA and "SELECT ... LIMIT" in MySQL or function "length" in ASA 8.0.3 and "len" in MS-SQL (SA 11.0.1 seems to support "len", too, but will process it locally with the default MS SQL capabilities).