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

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几个left join 连一块，读起来比较费劲，不知从何下手?