无法在 CTE 中使用 INSERT

Question

我正在尝试使用 CTE 将一些随机数据插入表中 -

create table foo (id integer)

with x as (select random())
  insert into foo (id)
  select x from x

这给出了一个错误： ERROR: column "id" is of type integer but expression is of type record

只是 CTE 的select作品：

with x as (select random())
--   insert into foo (id)
  select x from x

我也无法打字：

with x as (select random())
  insert into foo (id)
  select x::integer from x

这给出了一个错误：ERROR: cannot cast type record to integer。

出了什么问题以及如何解决？

Answer 1

select x from x

表示选择整行作为列（请注意输出中的括号，而不是纯数字）。就像复合类型的值一样。

例如，

melkij=> select pg_am.* from pg_am limit 1;
 oid | amname |      amhandler       | amtype 
-----+--------+----------------------+--------
   2 | heap   | heap_tableam_handler | t

melkij=> select pg_am from pg_am limit 1;
              pg_am              
---------------------------------
 (2,heap,heap_tableam_handler,t)

要获取函数的值，您需要访问特定列，而不是整行。

with x as (select random()) select x.random from x;
-- or
with x as (select random() as r) select r from x;
-- or
with x(r) as (select random()) select r from x;

您可以使用插入中的值

with x as (select random() as r)
  insert into foo (id)
  select r from x;