Fixed dbt view rename issue where ALTER TABLE ... RENAME TO fails on views because DuckDB requires ALTER VIEW. (#68)

Author: bill-ph

server/conn.go

@@ -380,11 +380,19 @@ func (c *clientConn) handleQuery(body []byte) error {
 
 		result, err := c.db.Exec(query)
 		if err != nil {
-			c.sendError("ERROR", "42000", err.Error())
-			c.setTxError()
-			writeReadyForQuery(c.writer, c.txStatus)
-			c.writer.Flush()
-			return nil
+			// Retry ALTER TABLE as ALTER VIEW if target is a view
+			if isAlterTableNotTableError(err) {
+				if alteredQuery, ok := transpiler.ConvertAlterTableToAlterView(query); ok {
+					result, err = c.db.Exec(alteredQuery)
+				}
+			}
+			if err != nil {
+				c.sendError("ERROR", "42000", err.Error())
+				c.setTxError()
+				writeReadyForQuery(c.writer, c.txStatus)
+				c.writer.Flush()
+				return nil
+			}
 		}
 
 		c.updateTxStatus(cmdType)
@@ -1561,10 +1569,18 @@ func (c *clientConn) handleExecute(body []byte) {
 		// Non-result-returning query: use Exec with converted query
 		result, err := c.db.Exec(p.stmt.convertedQuery, args...)
 		if err != nil {
-			log.Printf("[%s] Execute error: %v", c.username, err)
-			c.sendError("ERROR", "42000", err.Error())
-			c.setTxError()
-			return
+			// Retry ALTER TABLE as ALTER VIEW if target is a view
+			if isAlterTableNotTableError(err) {
+				if alteredQuery, ok := transpiler.ConvertAlterTableToAlterView(p.stmt.convertedQuery); ok {
+					result, err = c.db.Exec(alteredQuery, args...)
+				}
+			}
+			if err != nil {
+				log.Printf("[%s] Execute error: %v", c.username, err)
+				c.sendError("ERROR", "42000", err.Error())
+				c.setTxError()
+				return
+			}
 		}
 		c.updateTxStatus(cmdType)
 		tag := c.buildCommandTag(cmdType, result)
@@ -1689,3 +1705,12 @@ func readCString(r *bytes.Reader) (string, error) {
 	}
 	return buf.String(), nil
 }
+
+// isAlterTableNotTableError checks if the error indicates that an ALTER TABLE
+// was attempted on a view. DuckDB returns this error when trying to use
+// ALTER TABLE ... RENAME TO on a view instead of ALTER VIEW.
+func isAlterTableNotTableError(err error) bool {
+	msg := strings.ToLower(err.Error())
+	return strings.Contains(msg, "cannot use alter table") &&
+		strings.Contains(msg, "not a table")
+}

transpiler/transpiler.go

@@ -182,3 +182,40 @@ func (t *Transpiler) TranspileMulti(sql string) ([]*Result, error) {
 
 	return results, nil
 }
+
+// ConvertAlterTableToAlterView transforms an ALTER TABLE RENAME statement
+// to ALTER VIEW RENAME. This is used to retry failed ALTER TABLE commands
+// when DuckDB reports that the target is a view, not a table.
+// Returns the transformed SQL and true if successful, or the original SQL
+// and false if the input is not an ALTER TABLE RENAME statement.
+func ConvertAlterTableToAlterView(sql string) (string, bool) {
+	tree, err := pg_query.Parse(sql)
+	if err != nil || len(tree.Stmts) == 0 {
+		return sql, false
+	}
+
+	stmt := tree.Stmts[0].Stmt
+	if stmt == nil {
+		return sql, false
+	}
+
+	renameStmt, ok := stmt.Node.(*pg_query.Node_RenameStmt)
+	if !ok || renameStmt.RenameStmt == nil {
+		return sql, false
+	}
+
+	// Only transform if it's an ALTER TABLE RENAME (renameType == OBJECT_TABLE)
+	if renameStmt.RenameStmt.RenameType != pg_query.ObjectType_OBJECT_TABLE {
+		return sql, false
+	}
+
+	// Change to ALTER VIEW
+	renameStmt.RenameStmt.RenameType = pg_query.ObjectType_OBJECT_VIEW
+	renameStmt.RenameStmt.RelationType = pg_query.ObjectType_OBJECT_VIEW
+
+	result, err := pg_query.Deparse(tree)
+	if err != nil {
+		return sql, false
+	}
+	return result, true
+}

transpiler/transpiler_test.go

@@ -936,3 +936,82 @@ func TestTranspile_JSONOperators(t *testing.T) {
 		})
 	}
 }
+
+func TestConvertAlterTableToAlterView(t *testing.T) {
+	tests := []struct {
+		name       string
+		input      string
+		wantSQL    string
+		wantOK     bool
+		wantChange bool // whether output should differ from input
+	}{
+		{
+			name:       "ALTER TABLE RENAME to ALTER VIEW RENAME",
+			input:      `ALTER TABLE "my_schema"."my_view__tmp" RENAME TO "my_view"`,
+			wantOK:     true,
+			wantChange: true,
+		},
+		{
+			name:       "simple ALTER TABLE RENAME",
+			input:      `ALTER TABLE myview RENAME TO newname`,
+			wantOK:     true,
+			wantChange: true,
+		},
+		{
+			name:       "non-rename ALTER TABLE unchanged",
+			input:      `ALTER TABLE users ADD COLUMN email TEXT`,
+			wantOK:     false,
+			wantChange: false,
+		},
+		{
+			name:       "SELECT statement unchanged",
+			input:      `SELECT * FROM users`,
+			wantOK:     false,
+			wantChange: false,
+		},
+		{
+			name:       "CREATE TABLE unchanged",
+			input:      `CREATE TABLE users (id INT)`,
+			wantOK:     false,
+			wantChange: false,
+		},
+		{
+			name:       "empty string",
+			input:      ``,
+			wantOK:     false,
+			wantChange: false,
+		},
+		{
+			name:       "invalid SQL",
+			input:      `NOT VALID SQL AT ALL`,
+			wantOK:     false,
+			wantChange: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, ok := ConvertAlterTableToAlterView(tt.input)
+			if ok != tt.wantOK {
+				t.Errorf("ConvertAlterTableToAlterView(%q) ok = %v, want %v", tt.input, ok, tt.wantOK)
+			}
+			if tt.wantChange {
+				if result == tt.input {
+					t.Errorf("ConvertAlterTableToAlterView(%q) should change the SQL", tt.input)
+				}
+				// Check that it contains ALTER VIEW
+				if !strings.Contains(strings.ToUpper(result), "ALTER VIEW") {
+					t.Errorf("ConvertAlterTableToAlterView(%q) = %q, should contain ALTER VIEW", tt.input, result)
+				}
+				// Check that it does NOT contain ALTER TABLE
+				if strings.Contains(strings.ToUpper(result), "ALTER TABLE") {
+					t.Errorf("ConvertAlterTableToAlterView(%q) = %q, should not contain ALTER TABLE", tt.input, result)
+				}
+			} else {
+				if result != tt.input {
+					t.Errorf("ConvertAlterTableToAlterView(%q) = %q, should return original", tt.input, result)
+				}
+			}
+		})
+	}
+}