googleapis/mcp-toolbox · error

errors encountered when converting values

Error message

errors encountered when converting values: %w

What it means

This error is returned when mysqlcommon.ConvertToType fails to convert a raw driver value ([]byte) into the appropriate Go type for the column's declared type. The library scans values as raw bytes and converts them afterwards; when a value does not fit the column type reported by the server, conversion fails and the whole query result is abandoned.

Solutions

1. Fix the offending data at the source (the wrapped error identifies the column/value).
2. Sanitize in SQL: use NULLIF, COALESCE, or CAST to avoid unparseable temporal/numeric values.
3. Configure the MySQL server for zero-date handling that matches expectations (sql_mode NO_ZERO_DATE / convert zero dates).
4. If driver conversion rules are the issue, upgrade github.com/go-sql-driver/mysql and the common conversion package.

Example fix

// before
SELECT updated_at FROM legacy_orders;
// after
SELECT NULLIF(updated_at, '0000-00-00 00:00:00') AS updated_at FROM legacy_orders;

// Check temporal/numeric columns for unparseable values before conversion:
var bad int
err := db.QueryRow(`SELECT COUNT(*) FROM t WHERE updated_at = '0000-00-00 00:00:00' OR updated_at IS NULL`).Scan(&bad)
if err != nil { return err }
if bad > 0 {
    return fmt.Errorf("%d rows contain zero-dates; clean them or NULLIF in the query", bad)
}

out, err := toolboxClient.InvokeTool(ctx, "run-sql", params)
if err != nil && strings.Contains(err.Error(), "errors encountered when converting values") {
    // the wrapped error names the column/value; rewrite query with NULLIF/COALESCE and retry
    return fmt.Errorf("value conversion failed: %w", err)
}

When it happens

Trigger: Running a query through the mysql run-sql tool where a returned column's value cannot be parsed according to its MySQL column type — e.g. a TIME value out of range, an invalid DATE/DATETIME string, or a numeric column containing non-numeric data.

Common situations: Servers returning zero or out-of-range temporal values ('0000-00-00', '803:20:05') with strict parsing enabled via parseTime=true, corrupted data in legacy tables, or replicas with divergent column types from the primary.

Related errors

• errors encountered when converting values
• unable to parse row
• errors encountered during row iteration
• unable to connect successfully
• unable to create pool

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/898c8de987f7dcf2. Report an issue: GitHub.

Appendix: source

Thrown at internal/sources/mysql/mysql.go:172

	}

	out := []any{}
	for results.Next() {
		err := results.Scan(values...)
		if err != nil {
			return nil, fmt.Errorf("unable to parse row: %w", err)
		}
		row := orderedmap.Row{}
		for i, name := range cols {
			val := rawValues[i]
			if val == nil {
				row.Add(name, nil)
				continue
			}

			convertedValue, err := mysqlcommon.ConvertToType(colTypes[i], val)
			if err != nil {
				return nil, fmt.Errorf("errors encountered when converting values: %w", err)
			}
			row.Add(name, convertedValue)
		}
		out = append(out, row)
	}

	if err := results.Err(); err != nil {
		return nil, fmt.Errorf("errors encountered during row iteration: %w", err)
	}

	return out, nil
}

func initMySQLConnectionPool(ctx context.Context, tracer trace.Tracer, name, host, port, user, pass, dbname, queryTimeout string, queryParams map[string]string) (*sql.DB, error) {
	//nolint:all // Reassigned ctx
	ctx, span := sources.InitConnectionSpan(ctx, tracer, SourceType, name)
	defer span.End()

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