Re: Fix array-element quoting in postgres_fdw import statistics

On Sun, Apr 12, 2026 at 12:13 PM SATYANARAYANA NARLAPURAM
<satyanarlapuram(at)gmail(dot)com> wrote:
> build_remattrmap() used quote_identifier() to format column names
> for a text[] array literal passed to the remote pg_stats query.
> quote_identifier() applies SQL identifier quoting, which doubles
> double-quote characters but does not escape backslashes. However,
> inside a PostgreSQL array literal, backslash is an escape character.
>
> Column names containing backslashes (e.g. "a\b") were silently
> mangled by the array parser—"a\b" became "ab"—causing the
> WHERE attname = ANY('{...}') filter to miss those columns. The
> statistics import would then fail with a WARNING about missing
> attribute statistics. This is a very corner cases because usually
> backslash is not included in the column names. Anyways attached
> a draft patch. Please take a look and let me know what you think.
>
> -- Setup
> CREATE TABLE bs_test (id int PRIMARY KEY, "a\b" int, normal_col text);
> INSERT INTO bs_test SELECT g, g, 'val' FROM generate_series(1,1000) g;
> ANALYZE bs_test;
>
> CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw
> OPTIONS (host '127.0.0.1', port '5432', dbname 'testdb', restore_stats 'true');
> CREATE USER MAPPING FOR CURRENT_USER SERVER loopback OPTIONS (user 'postgres');
>
> CREATE FOREIGN TABLE fbs_test (id int, "a\b" int, normal_col text)
> SERVER loopback OPTIONS (schema_name 'public', table_name 'bs_test');
>
> ANALYZE fbs_test;
> -- WARNING: could not import statistics for foreign table "public.fbs_test"
> --- no attribute statistics found for column "a\b" of remote table "public.bs_test"

Good catch! I will look into this as well. I added it to the open
items list as well.

Thanks for the report and patch, again!

Best regards,
Etsuro Fujita