使用同一个表中的SubQuery进行更新

Question

是否可以使用同一个表中的子查询进行更新？

我收到此错误：

1093 - 您无法指定目标表＆＃39;任务＆＃39;用于FROM子句

中的更新

update tasks SET completed_form = 'y' AND all_forms_in = 'y' where EID in (select EID from tasks WHERE completed_form = 'y' AND all_forms_in = 'n' group by EID having count(*) > 1);

更新

我发现，如果我将查询包装在另一个选择中，那么它是否有效。这里引用：MySQL Error 1093 - Can't specify target table for update in FROM clause

update tasks SET all_forms_in = 'y' where EID in (SELECT * FROM (select EID from tasks WHERE completed_form = 'y' AND all_forms_in = 'n' group by EID having count(*) > 1)AS b);

Answer 1

MySQL在UPDATE语句中支持JOIN，因此您可以在没有子查询的情况下执行此操作。您必须使用已完成的条件加入两个不同的行，以模拟计数（*）＆gt; 1。

UPDATE tasks AS t1
INNER JOIN tasks AS t2
  ON (t1.EID = t2.EID AND t2.completed_form = 'y' AND t2.all_forms_in = 'n')
INNER JOIN tasks AS t3
  ON (t1.EID = t3.EID AND t3.completed_form = 'y' AND t3.all_forms_in = 'n'
  AND t2.primary_key <> t3.primary_key)
SET t1.completed_form = 'y', 
    t1.all_forms_in = 'y';