From: "Tatsuo Ishii" <is...@postgresql.org>
I don't think the bind placeholder is the case. That is processed by exec_bind_message() in postgres.c. It has enough info about the type of the placeholder, and I think we can easily deal with NCHAR. Same thing can be said to COPY case.
Yes, I've learned it. Agreed. If we allow an encoding for NCHAR different from the database encoding, we can convert text from the client encoding to the NCHAR encoding in nchar_in() for example. We can retrieve the NCHAR encoding from pg_database and store it in a global variable at session start.
Problem is an ordinary query (simple protocol "Q" message) as you pointed out. Encoding conversion happens at a very early stage (note that fast-path case has the same issue). If a query message contains, say, SHIFT-JIS and EUC-JP, then we are going into trouble because the encoding conversion routine (pg_client_to_server) regards that the message from client contains only one encoding. However my question is, does it really happen? Because there's any text editor which can create SHIFT-JIS and EUC-JP mixed text. So my guess is, when user want to use NCHAR as SHIFT-JIS text, the rest of query consist of either SHIFT-JIS or plain ASCII. If so, what the user need to do is, set the client encoding to SJIFT-JIS and everything should be fine. Maumau, is my guess correct?
Yes, I believe you are right. Regardless of whether we support multiple encodings in one database or not, a single client encoding will be sufficient for one session. When receiving the "Q" message, the whole SQL text is converted from the client encoding to the database encoding. This part needs no modification. During execution of the "Q" message, NCHAR values are converted from the database encoding to the NCHAR encoding.
Thank you very much, Tatsuo san. Everybody, is there any other challenge we should consider to support NCHAR/NVARCHAR types as distinct types?
Regards MauMau -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
