Pass through DuckDB SHOW commands (TABLES, DATABASES, ALL) (#268)

SHOW TABLES, SHOW DATABASES, and SHOW ALL were being rejected with
"unrecognized configuration parameter" because the transpiler's
catch-all treated any single-word SHOW argument as a PostgreSQL
config parameter. These are valid DuckDB commands that return
result sets and should be forwarded to DuckDB unchanged.

Author: jghoman

transpiler/transform/setshow.go

@@ -12,6 +12,14 @@ import (
 // (lowercase letters, digits, and underscores, starting with a letter)
 var configParamPattern = regexp.MustCompile(`^[a-z][a-z0-9_]*$`)
 
+// duckdbShowCommands are DuckDB-specific SHOW commands that should be passed
+// through to DuckDB rather than treated as PostgreSQL config parameters.
+var duckdbShowCommands = map[string]bool{
+	"tables":    true,
+	"databases": true,
+	"all":       true,
+}
+
 // SetShowTransform handles SET and SHOW commands:
 // - SET application_name = 'x' -> SET VARIABLE application_name = 'x'
 // - SHOW application_name -> SELECT getvariable('application_name') AS application_name
@@ -277,6 +285,13 @@ func (t *SetShowTransform) Transform(tree *pg_query.ParseResult, result *Result)
 					continue
 				}
 
+				// DuckDB SHOW commands (SHOW TABLES, SHOW DATABASES, SHOW ALL TABLES)
+				// are parsed as VariableShowStmt by pg_query but should be passed
+				// through to DuckDB as-is.
+				if duckdbShowCommands[paramName] {
+					continue
+				}
+
 				// If this looks like a PostgreSQL config parameter (e.g., "some_setting")
 				// but we don't recognize it, return an error rather than letting DuckDB
 				// give a confusing "table not found" error

transpiler/transpiler_test.go

@@ -690,6 +690,46 @@ func TestTranspile_SetShow(t *testing.T) {
 		}
 	})
 
+	// Test DuckDB SHOW commands pass through unchanged
+	t.Run("SHOW TABLES passthrough", func(t *testing.T) {
+		result, err := tr.Transpile("SHOW TABLES")
+		if err != nil {
+			t.Fatalf("Transpile error: %v", err)
+		}
+		if result.Error != nil {
+			t.Fatalf("SHOW TABLES should not error, got: %v", result.Error)
+		}
+		if !strings.Contains(strings.ToUpper(result.SQL), "SHOW TABLES") {
+			t.Errorf("SHOW TABLES should pass through, got: %q", result.SQL)
+		}
+	})
+
+	t.Run("SHOW DATABASES passthrough", func(t *testing.T) {
+		result, err := tr.Transpile("SHOW DATABASES")
+		if err != nil {
+			t.Fatalf("Transpile error: %v", err)
+		}
+		if result.Error != nil {
+			t.Fatalf("SHOW DATABASES should not error, got: %v", result.Error)
+		}
+		if !strings.Contains(strings.ToUpper(result.SQL), "SHOW DATABASES") {
+			t.Errorf("SHOW DATABASES should pass through, got: %q", result.SQL)
+		}
+	})
+
+	t.Run("SHOW ALL passthrough", func(t *testing.T) {
+		result, err := tr.Transpile("SHOW ALL")
+		if err != nil {
+			t.Fatalf("Transpile error: %v", err)
+		}
+		if result.Error != nil {
+			t.Fatalf("SHOW ALL should not error, got: %v", result.Error)
+		}
+		if !strings.Contains(strings.ToUpper(result.SQL), "SHOW ALL") {
+			t.Errorf("SHOW ALL should pass through, got: %q", result.SQL)
+		}
+	})
+
 	// Test SET application_name is ignored
 	t.Run("SET application_name ignored", func(t *testing.T) {
 		result, err := tr.Transpile("SET application_name = 'fivetran'")