Question

以下 PostgreSQL 查询有什么问题？

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

给出

[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

我试过了，

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

给出

[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

正确的语法是什么？

Answer 1

要避免两个问题：

1-在SET列=值中，不要在column前添加表名或别名。它产生错误并且无论如何都是无用的，因为UPDATE tablename只能从tablename更新列。 tablename的别名可以在其他地方使用，但不能在SET子句中使用。

2-不要在查询的其余部分重复要更新的表名，除非您要特别引发该表的二次和不相关扫描。

以下是我提出的修改后的查询建议，希望能满足您的要求：

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);

如何使用JOIN将列从一个表复制到另一个表

1 个答案: