Fix UNKNOWN parameter type error for params used in expressions

include/pgduckdb/pgduckdb_ruleutils.h

@@ -21,6 +21,7 @@ bool pgduckdb_is_duckdb_row(Oid type_oid);
 bool pgduckdb_is_unresolved_type(Oid type_oid);
 bool pgduckdb_is_fake_type(Oid type_oid);
 bool pgduckdb_var_is_duckdb_row(Var *var);
+void pgduckdb_get_param(StringInfo buf, Param *param);
 bool pgduckdb_func_returns_duckdb_row(RangeTblFunction *rtfunc);
 Var *pgduckdb_duckdb_subscript_var(Expr *expr);
 bool pgduckdb_reconstruct_star_step(StarReconstructionContext *ctx, ListCell *tle_cell);

src/pgduckdb_ruleutils.cpp

@@ -98,6 +98,25 @@ pgduckdb_is_fake_type(Oid type_oid) {
 	return false;
 }
 
+/*
+ * Deparse an external parameter as CAST($n AS <type>) instead of a bare $n.
+ * DuckDB can't always infer a parameter's type (e.g. inside "$1 + 1"), leaving
+ * it UNKNOWN and unconvertible to a Postgres type (issue #480); the cast hands
+ * it the type Postgres already resolved. Fake types are skipped (see above).
+ */
+void
+pgduckdb_get_param(StringInfo buf, Param *param) {
+	Oid paramtype = param->paramtype;
+
+	if (param->paramkind == PARAM_EXTERN && OidIsValid(paramtype) && paramtype != UNKNOWNOID &&
+	    !pgduckdb_is_fake_type(paramtype)) {
+		appendStringInfo(buf, "CAST($%d AS %s)", param->paramid,
+		                 format_type_with_typemod(paramtype, param->paramtypmod));
+	} else {
+		appendStringInfo(buf, "$%d", param->paramid);
+	}
+}
+
 static bool
 pgduckdb_is_duckdb_subscript_type(Oid type_oid) {
 	if (pgduckdb_is_unresolved_type(type_oid)) {

src/vendor/pg_ruleutils_14.c

@@ -8175,7 +8175,7 @@ get_parameter(Param *param, deparse_context *context)
 	/*
 	 * Not PARAM_EXEC, or couldn't find referent: just print $N.
 	 */
-	appendStringInfo(context->buf, "$%d", param->paramid);
+	pgduckdb_get_param(context->buf, param);
 }
 
 /*

src/vendor/pg_ruleutils_15.c

@@ -8378,7 +8378,7 @@ get_parameter(Param *param, deparse_context *context)
 	/*
 	 * Not PARAM_EXEC, or couldn't find referent: just print $N.
 	 */
-	appendStringInfo(context->buf, "$%d", param->paramid);
+	pgduckdb_get_param(context->buf, param);
 }
 
 /*

src/vendor/pg_ruleutils_16.c

@@ -8313,7 +8313,7 @@ get_parameter(Param *param, deparse_context *context)
 	/*
 	 * Not PARAM_EXEC, or couldn't find referent: just print $N.
 	 */
-	appendStringInfo(context->buf, "$%d", param->paramid);
+	pgduckdb_get_param(context->buf, param);
 }
 
 /*

src/vendor/pg_ruleutils_17.c

@@ -8515,7 +8515,7 @@ get_parameter(Param *param, deparse_context *context)
 	 */
 	Assert(param->paramkind == PARAM_EXTERN);
 
-	appendStringInfo(context->buf, "$%d", param->paramid);
+	pgduckdb_get_param(context->buf, param);
 }
 
 /*

src/vendor/pg_ruleutils_18.c

@@ -8863,7 +8863,7 @@ get_parameter(Param *param, deparse_context *context)
 	 */
 	Assert(param->paramkind == PARAM_EXTERN);
 
-	appendStringInfo(context->buf, "$%d", param->paramid);
+	pgduckdb_get_param(context->buf, param);
 }
 
 /*

src/vendor/pg_ruleutils_19.c

@@ -9438,7 +9438,7 @@ get_parameter(Param *param, deparse_context *context)
 	 */
 	Assert(param->paramkind == PARAM_EXTERN);
 
-	appendStringInfo(context->buf, "$%d", param->paramid);
+	pgduckdb_get_param(context->buf, param);
 }
 
 /*

test/pycheck/prepared_test.py

@@ -42,6 +42,64 @@ def test_prepared(cur: Cursor):
     assert cur.sql(q2, (4,)) == 0
 
 
+def test_prepared_param_in_expression(cur: Cursor):
+    # Regression test for issue #480: a parameter used inside an expression
+    # (rather than a direct comparison) cannot have its type inferred by DuckDB.
+    # We deparse it with an explicit cast so DuckDB knows the type instead of
+    # reporting it as UNKNOWN.
+    cur.sql("CREATE TEMP TABLE test_table (id int) USING duckdb")
+    cur.sql("INSERT INTO test_table VALUES (1), (2), (3)")
+
+    q = "SELECT count(*) FROM test_table WHERE id = %s + 1"
+
+    cur.sql("SET plan_cache_mode = 'force_custom_plan'")
+    assert cur.sql(q, (1,), prepare=True) == 1  # matches id = 2
+    assert cur.sql(q, (2,)) == 1  # matches id = 3
+    assert cur.sql(q, (3,)) == 0  # id = 4 does not exist
+
+    cur.sql("SET plan_cache_mode = 'force_generic_plan'")
+    assert cur.sql(q, (1,)) == 1  # creates generic plan
+    assert cur.sql(q, (2,)) == 1
+    assert cur.sql(q, (3,)) == 0
+
+
+def test_prepared_param_cast_types(cur: Cursor):
+    # Regression test for issue #480: every external parameter now deparses as
+    # CAST($n AS <pgtype>), so the emitted type name must be one DuckDB can parse.
+    # This covers more types than int, including the multi-word "timestamp with
+    # time zone".
+    cur.sql(
+        "CREATE TEMP TABLE test_table (t text, ts timestamptz, u uuid) USING duckdb"
+    )
+    u = uuid.UUID("12345678-1234-5678-1234-567812345678")
+    cur.sql(
+        "INSERT INTO test_table VALUES (%s, %s, %s)",
+        ("foo", datetime.datetime(2020, 1, 1, tzinfo=datetime.timezone.utc), u),
+    )
+
+    for mode in ("force_custom_plan", "force_generic_plan"):
+        cur.sql(f"SET plan_cache_mode = '{mode}'")
+        # text: parameter concatenated
+        assert (
+            cur.sql(
+                "SELECT count(*) FROM test_table WHERE t = %s || 'o'",
+                ("fo",),
+                prepare=True,
+            )
+            == 1
+        )
+        # timestamptz: parameter used in interval arithmetic
+        assert (
+            cur.sql(
+                "SELECT count(*) FROM test_table WHERE ts = %s + interval '1 day'",
+                (datetime.datetime(2019, 12, 31, tzinfo=datetime.timezone.utc),),
+            )
+            == 1
+        )
+        # uuid: cast is emitted even for a plain equality
+        assert cur.sql("SELECT count(*) FROM test_table WHERE u = %s", (u,)) == 1
+
+
 def test_extended(cur: Cursor):
     cur.sql("""
         CREATE TABLE t(
@@ -161,7 +219,7 @@ def test_prepared_ctas(cur: Cursor):
     # crash.
     with pytest.raises(
         psycopg.errors.InternalError,
-        match="Could not find parameter with identifier 1",
+        match="Not all parameters were bound",
     ):
         cur.sql(
             "CREATE TEMP TABLE t2 USING duckdb AS SELECT * FROM heapt where id = %s",