@Override
    public String getString(int columnIndex) throws SQLException {
        if (columnIndex < 1 || columnIndex > cachedColumnLabels.length) {
            throw new SQLException("Invalid column index: " + columnIndex);
        }
        return getString(cachedColumnLabels[columnIndex - 1]);
    }
Registers a transformer function for a given column.
The transformer takes the original String value and returns a new String.

@param columnLabel The name of the column (case-insensitive).
@param transformer The function that transforms the value.
jdbc-v2/src/main/java/com/clickhouse/jdbc/internal/MetadataResultSet.java