Question

我想用leaf_category更新列TRUE，其中类别不是父类别。它作为一个选择语句：

 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;

但是，相应的UPDATE会将所有列设置为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;

这样的UPDATE是否可能？

Answer 1

您只是缺少连接的WHERE子句：

UPDATE catalog_category 
SET    leaf_category = TRUE
FROM   catalog_category c1 
LEFT   join catalog_category c2 ON c1.id = c2.parent_id
WHERE  catalog_category.id = c1.id
AND    c2.parent_id IS NULL;

这个带有NOT EXISTS的表格可能更快，同时也是这样：

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

PostgreSQL：忽略左外部自连接的更新

1 个答案: