Hi All,
Consider following sequence of commands
create type complex as (r float8, i float8);
create type quad as (c1 complex, c2 complex);
create temp table quadtable(f1 int, q quad);
insert into quadtable (f1, q.c1.r, q.c2.i) values(44,55,66);
While parsing the INSERT query, we parse the query with three columns and
three values in the target list, but during rewriting we combine q.c1.r and
q.c2.i into a single column in the form of FieldStore structure. In
Postgres-XC, we deparse these parse trees, to be sent to other PostgreSQL
servers. The function processIndirection(), which deparses the
indirections, can not handle more than one field in FieldStore node.
7344 /*
7345 * Print the field name. There should only be one target
field in
7346 * stored rules. There could be more than that in
executable
7347 * target lists, but this function cannot be used for that
case.
7348 */
7349 Assert(list_length(fstore->fieldnums) == 1);
7350 fieldname = get_relid_attribute_name(typrelid,
7351
linitial_int(fstore->fieldnums));
7352 if (printit)
7353 appendStringInfo(buf, ".%s",
quote_identifier(fieldname));
Why is this restriction here?
The assertion is added by commit 858d1699. The notes for the commit have
following paragraph related to FieldStore deparsing.
I chose to represent an assignment ArrayRef as "array[subscripts] :=
source",
which is fairly reasonable and doesn't omit any information. However,
FieldStore is problematic because the planner will fold multiple
assignments
to fields of the same composite column into one FieldStore, resulting
in a
structure that is hard to understand at all, let alone display
comprehensibly.
So in that case I punted and just made it print the source
expression(s).
So, there doesn't seem to be any serious reason behind the restriction.
--
Best Wishes,
Ashutosh Bapat
EntepriseDB Corporation
The Enterprise Postgres Company
