Redshift - ERROR: Target table must be part of an equijoin predicate - sql

Question

I am trying to make an update on a temporal table I created in Redshift. The code I am trying to run goes like this:
UPDATE #new_emp
SET rpt_to_emp_id = CAST(ht.se_value AS INTEGER),
rpt_to_extrnl_email = ht.extrnl_email_addr,
rpt_to_fst_nm = ht.first_nm,
rpt_to_lst_nm = ht.last_nm,
rpt_to_mdl_init = ht.mdl_nm,
rpt_to_nm = ht.full_nm,
rpt_to_ssn = CAST(ht.ssn AS INTEGER),
FROM #new_emp,
(SELECT DISTINCT t.se_value,h.first_nm,h.last_nm,
h.mdl_nm,h.full_nm,h.ssn,h.extrnl_email_addr
FROM spec_hr.dtbl_translate_codes_dw t, spec_hr.emp_hron h
WHERE t.inf_name = 'system'
AND t.fld_name = 'HRONDirector'
AND h.foreign_emp_id = t.se_value
) ht
WHERE #new_emp.foreign_emp_id <> ht.se_value
AND (#new_emp.emp_status_cd <> 'T'
AND (#new_emp.ult_rpt_emp_id = #new_emp.foreign_emp_id
OR #new_emp.ult_rpt_emp_id = #new_emp.psoft_id
OR #new_emp.ult_rpt_emp_id IS NULL));
I've tried both with and without specyfing the updated table from the FROM command. But it keeps throwing me this error:
ERROR: Target table must be part of an equijoin predicate
Any ideas why is this failing? Thank you!

Answer 1

Redshift needs an equality join condition to know what value to update and with which values. Your join condition is "#new_emp.foreign_emp_id <> ht.se_value" which is an inequality or Redshift speak - this is not "an equijoin predicate". You have a SET of "rpt_to_lst_nm = ht.last_nm" but if the only join condition is an inequality then which value of last_nm is Redshift putting in the table?
To put it the other way around - you need to tell Redshift exactly which rows of the target table are receiving which values (equijoin). The join condition you have doesn't meet this requirement.