$where['a.status'] = ['lt', 4];  
$where['o.bonustime'] = 0;  
$where[] = ['exp', "CAST(COALESCE(JSON_UNQUOTE(JSON_EXTRACT(a.ratejson, '$.rate1')), '0') AS DECIMAL(10,3)) > 0"];

ratejson字段为text字段或者JSON字段