几个left join连接起来表示什么意思?

首先看一段代码：

select  sar.markerallel1 || sar.markerallel2 as markeralleleselements,
       sg.auditor,
       si.*,
       sar.*,
       ci.*
  from sample_info si
  left join sample_audit_result sar on si.sample_id = sar.sample_id
  left join case_info ci on ci.case_id = si.case_id
  left join sample_gene sg on si.sample_id = sg.sample_id
 where si.IS_DELETED <> 1
   and si.ACCEPT_STATUS = 1
   and sg.audit_status = '1'
   and si.case_id in
       (select case_id
          from case_info
         where case_base_info_id in
               (select case_base_info_id
                  from case_info
                 where case_id = '04dd3a01-e6a3-4489-a694-f8daf3e36cc8'))
   and sg.id in (select sample_gene_id from sample_audit_result sar)
   and si.barcode in (select sample_barcode from sample_audit_result sar)
 order by length(si.barcode), si.bar

 

几个left join 连一块，读起来比较费劲，不知从何下手?