Fix Could not convert DuckDB type: UNKNOWN to Postgres type for parameters used in expressions - #1062
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Parameters used inside an expression (e.g. `WHERE id = $1 + 1`) could not have their type inferred by DuckDB at plan time, failing with "Could not convert DuckDB type: UNKNOWN". Deparse external parameters as CAST($n AS <type>) so DuckDB gets the type Postgres already resolved. Fixes duckdb#480.
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A prepared or parameterized statement fails when a bind parameter is used inside an expression, e.g.
SELECT count(*) FROM t WHERE id = $1 + 1:pg_duckdb deparses the query and calls DuckDB
Prepare()at plan time to learn the result types. DuckDB can't infer a parameter's type inside an expression, so it staysUNKNOWNand result-type resolution fails (same root cause as #396). Since Postgres already resolved the parameter's type, we now deparse each external parameter asCAST($n AS <pgtype>)instead of a bare$n, handing DuckDB the type it needs. A regression test is included.This also changes the error for CTAS-with-a-parameter (still unsupported): the parameter now gets a type, so DuckDB fails later with "Not all parameters were bound" instead of "Could not find parameter with identifier 1" -- same clean failure, different message.
Known limitation:
jsonbparameters still fail (CAST($n AS jsonb)-- DuckDB has nojsonbtype); pre-existing, tracked in #516.Fixes #480.