Question

What is wrong with the following PostgreSQL query?

UPDATE project_project SET  project_project.create_date = assignments.start_date  
FROM project_project
LEFT JOIN account_analytic_account ON account_analytic_account.id = project_project.analytic_account_id
LEFT JOIN assignments ON assignments.accounts_ref = account_analytic_account.id

gives

[SQL] UPDATE project_project SET  project_project.create_date = assignments.start_date  
FROM project_project
LEFT JOIN account_analytic_account ON account_analytic_account.id = project_project.analytic_account_id
LEFT JOIN assignments ON assignments.accounts_ref = account_analytic_account.id

[Err] ERROR:  table name "project_project" specified more than once

I tried,

UPDATE pp SET  pp.create_date = am.start_date  
FROM project_project as pp
LEFT JOIN account_analytic_account as aa ON aa.id = pp.analytic_account_id
LEFT JOIN assignments as am ON am.accounts_ref = aa.id

gives

[SQL] UPDATE pp SET  pp.create_date = am.start_date  
FROM project_project pp
LEFT JOIN account_analytic_account aa ON aa.id = pp.analytic_account_id
LEFT JOIN am ON am.accounts_ref = aa.account_analytic_account.id

[Err] ERROR:  relation "pp" does not exist
LINE 1: UPDATE pp SET  pp.create_date = am.start_date  

What is the correct syntax?

Answer 1

There are two problems to avoid:

1- in SET column=value, do not prepend a table name or alias to column. It yields an error and is useless anyway, since UPDATE tablename is only able to update columns from tablename. An alias of tablename can be used in other places, but not in the SET clause.

2- don’t repeat the name of the table to update in the rest of the query unless you want to specifically induce a secondary and uncorrelated scan of this table.

Here is my proposal of a modified query that I hope does what you intend:

UPDATE project_project pp SET create_date =
 (select assignments.start_date  FROM account_analytic_account LEFT JOIN assignments
  ON assignments.accounts_ref = account_analytic_account.id
 WHERE 
 account_analytic_account.id = pp.analytic_account_id);