Re: [I] Superset is adding the escape character for '\' character in filter value, resulting to zero records filtered [superset]

["kokhlo (via GitHub)" <gi...@apache.org>]

kokhlo commented on issue #38453:
URL: https://github.com/apache/superset/issues/38453#issuecomment-6102982564

   Root cause found — it is not DuckDB adding the escape, it is SQLAlchemy's dialect default leaking through.
   
   duckdb-engine subclasses the psycopg2 PostgreSQL dialect, whose class-level `_backslash_escapes` default is `True`. PostgreSQL corrects this per-connection by probing `standard_conforming_strings` (`_set_backslash_escapes`), but DuckDB has no such knob and never runs that probe, so the flag stays `True` forever. Superset compiles filter values with `literal_binds` (`Database.compile_sqla_query`), so `name\email` renders as `'name\\email'` — which real DuckDB reads as a literal two-backslash string that matches nothing.
   
   Verified on the pinned versions (sqlalchemy 2.0.52, duckdb-engine 0.17.0, live in-process DuckDB): `SELECT 'name\\email' = 'name\email'` → False.
   
   Fix in #45180: `DuckDBEngineSpec.register_engine_events` sets `engine.dialect._backslash_escapes = False` — the same correction `_normalize_postgresql_backslash_escapes` already applies for PostgreSQL on the Jinja path, but the main compile path had no equivalent for duckdb. Regression tests included (one unit, one end-to-end against live DuckDB).


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