使用 CTE 删除似乎不起作用

Question

我有以下使用多个 CTE 的查询：

;with Test as (select plan_id, max("id") maxid
from Scheme
group by plan_id),
Rec as (select rh.* from Scheme rh, Test
where rh.plan_id = Test.plan_id
and rh.id = Test.maxid
and rh.event_id = 20)
delete from Scheme rh USING Rec
where rh.id = "Rec".id;

我收到以下错误：

[Err] ERROR:  missing FROM-clause entry for table "Rec"
LINE 9: where rh.id = "Rec".id;

如果我仅使用一个 CTE 重写查询，则 delete from "table" USING "CTE" 语法有效。我在上述查询中遗漏了什么？

Answer 1

您可以通过两种方式执行此操作。

使用IN运算符删除记录。

WITH Test
     AS (SELECT plan_id,
                Max("id") maxid
         FROM   Scheme
         GROUP  BY plan_id),
     Rec
     AS (SELECT rh.*
         FROM   Scheme rh,
                Test
         WHERE  rh.plan_id = Test.plan_id
                AND rh.id = Test.maxid
                AND rh.event_id = 20)
DELETE FROM Scheme
WHERE  id IN(SELECT a.id
             FROM   rec a);

或者通过使用 join 也可以做到这一点，但是 Using 构造将具有两个 table 之间的公共列，而不是 table 名称。

WITH Test
     AS (SELECT plan_id,
                Max("id") maxid
         FROM   Scheme
         GROUP  BY plan_id),
     Rec
     AS (SELECT rh.*
         FROM   Scheme rh,
                Test
         WHERE  rh.plan_id = Test.plan_id
                AND rh.id = Test.maxid
                AND rh.event_id = 20)
DELETE FROM Scheme join rec using(id);

Answer 2

错误的实际原因是无端大写加上不正确的引用：

...
delete from Scheme rh USING <b>Rec</b>
where rh.id = <b>"Rec"</b>.id;

未加引号的标识符在 Postgres 中被强制转换为小写并且有效地不区分大小写。如果双引号，则需要匹配大小写。 "Rec" 与 Rec 不同。详情：

Are PostgreSQL column names case-sensitive?

你的声明已清理：

WITH test AS (
   SELECT plan_id, max(id) AS id
   FROM   scheme
   GROUP  BY plan_id
   )
,  rec AS (
   SELECT s.*
   FROM   scheme s
   JOIN   test   t USING (plan_id, id)
   WHERE  s.event_id = 20
   )
DELETE FROM scheme s
USING  rec
WHERE  s.id = rec.id;

但这相当低效。有更好的方法来识别每个 plan_id.

具有最大 id 的行

更短更快 DISTINCT ON 和子查询而不是 CTE:

DELETE FROM scheme s
USING (
   SELECT DISTINCT ON (plan_id)
          plan_id, id, event_id 
   FROM   scheme
   ORDER  BY plan_id, id DESC NULLS LAST
   ) r
WHERE  r.event_id = 20
AND    s.id = r.id;

DISTINCT ON 的详细信息：

Select first row in each GROUP BY group?

使用 CTE 删除似乎不起作用

DELETE using CTEs does not seem to work

sql

postgresql

greatest-n-per-group

identifier

sql-delete