presto-postgresql/src/main/java/io/prestosql/plugin/postgresql/PostgreSqlClient.java/PostgreSqlClient/jsonColumnMapping
class PostgreSqlClient:    private ColumnMapping jsonColumnMapping()
    {
        return ColumnMapping.sliceMapping(
                jsonType,
                (resultSet, columnIndex) -> jsonParse(utf8Slice(resultSet.getString(columnIndex))),
                typedVarcharWriteFunction("json"),
                DISABLE_PUSHDOWN);
    }