PostgreSQL: update with left outer self join ignored

问题

I want to update the column leaf_category with TRUE where the category is not a parent category. It works as a select statement:

 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;

However, the corresponding UPDATE sets all the columns to 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 like that possible at all?

回答1:

You are just missing a connecting WHERE clause:

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;

This form with NOT EXISTS is probably faster, while doing the same:

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

来源：https://stackoverflow.com/questions/8766763/postgresql-update-with-left-outer-self-join-ignored