加入六个表在php和mysql中不起作用

Question

我正在尝试联接6个表，并希望显示payperiod_sdesc，gross_pay，esi_employer_contribution，pf_employer_contribution和employerContribution。

我从一开始就尝试过，但是加入起来很困难。我尝试了四个表联接，但剩下两个表我觉得很困难

left join 
py_process_labour_welfare
on
py_pay_group.pg_code = py_process_labour_welfare.pg_code

此连接行不起作用...

select payperiod_sdesc,gross_pay,esi_employer_contribution,employerContribution 
from py_process_emp_status_approved
left join py_process_tds_pf_pt 
  on py_process_emp_status_approved.ou_code = py_process_tds_pf_pt.ou_code
left join py_pay_group
  on py_process_tds_pf_pt.pg_code = py_pay_group.pg_code
left join py_process_labour_welfare
  on py_pay_group.pg_code = py_process_labour_welfare.pg_code
left join py_pay_period
  on py_process_labour_welfare.payperiod_code = py_pay_period.payperiod_code
left join py_payroll_calendar 
  on py_pay_period.paycal_code = py_payroll_calendar.paycal_code

我已经附上了所有六个表格图像链接。