PostgreSQL：忽略左外自连接更新

我要更新专栏leaf_category with TRUE其中类别不是父类别。它作为一个选择语句工作：

 select 
     c1.id, c1.name, c1.slug, c1.level, c2.parent_id, c2.name, c2.slug, c2.level 
 from
     catalog_category c1 
 left outer join 
     catalog_category c2 on 
     (c1.id = c2.parent_id)
 where 
     c2.parent_id is null;

然而，相应的UPDATE将所有列设置为TRUE.

update catalog_category 
set leaf_category = True
from
    catalog_category c1 
left outer join 
    catalog_category c2 on 
    (c1.id = c2.parent_id)
 where 
     c2.parent_id is null;

Is an UPDATE这样可能吗？

你只是缺少一个连接WHERE clause:

UPDATE catalog_category c
SET    leaf_category = true
FROM   catalog_category c1 
LEFT   JOIN catalog_category c2 ON c1.id = c2.parent_id
WHERE  c.id = c1.id
AND    c2.parent_id IS NULL;

这种形式与NOT EXISTS做同样的事情可能会更快：

UPDATE catalog_category c
SET    leaf_category = true
WHERE  NOT EXISTS (
    SELECT FROM catalog_category c1
    WHERE  c1.parent_id = c.id
    );

该手册用于UPDATE.

Related:

• 选择其他表中不存在的行