presto-main/src/main/java/io/prestosql/metadata/MetadataManager.java/MetadataManager/getColumnHandles
class MetadataManager:    @Override
    public Map<String, ColumnHandle> getColumnHandles(Session session, TableHandle tableHandle)
    {
        CatalogName catalogName = tableHandle.getCatalogName();
        ConnectorMetadata metadata = getMetadata(session, catalogName);
        Map<String, ColumnHandle> handles = metadata.getColumnHandles(session.toConnectorSession(catalogName), tableHandle.getConnectorHandle());

        ImmutableMap.Builder<String, ColumnHandle> map = ImmutableMap.builder();
        for (Entry<String, ColumnHandle> mapEntry : handles.entrySet()) {
            map.put(mapEntry.getKey().toLowerCase(ENGLISH), mapEntry.getValue());
        }
        return map.build();
    }