SQL - 使用 WITH 在 INSERT INTO 上声明变量

Question

在执行INSERT INTO 时，我正在尝试使用WITH 为查询声明一个变量。 我正在关注https://stackoverflow.com/a/16552441/2923526，它为SELECT 查询提供了以下示例：

WITH myconstants (var1, var2) as (
   values (5, 'foo')
)
SELECT *
FROM somewhere, myconstants
WHERE something = var1
   OR something_else = var2;

---

我尝试了以下方法，但没有成功：

playground> CREATE TABLE foo (id numeric)
CREATE TABLE

playground> WITH consts (x) AS (VALUES (2)) INSERT INTO foo VALUES (x)
column "x" does not exist
LINE 1: WITH consts (x) AS (VALUES (2)) INSERT INTO foo VALUES (x)
                                                                ^

playground> WITH consts (x) AS (VALUES (2)) INSERT INTO foo VALUES (consts.x)
missing FROM-clause entry for table "consts"
LINE 1: ...consts (x) AS (VALUES (2)) INSERT INTO foo VALUES (consts.x)
                                                              ^

playground> WITH consts (x) AS (VALUES (2)) INSERT INTO foo VALUES (consts.x) FROM consts
syntax error at or near "FROM"
LINE 1: ...AS (VALUES (2)) INSERT INTO foo VALUES (consts.x) FROM const...
                                                             ^

playground> WITH consts (x) AS (VALUES (2)) INSERT INTO foo FROM consts VALUES (consts.x)
syntax error at or near "FROM"
LINE 1: WITH consts (x) AS (VALUES (2)) INSERT INTO foo FROM consts ...
                                                        ^

---

注意我是 SQL 初学者，所以我希望避免使用 PLPGSQL 的解决方案

Answer 1

我认为你想要：

WITH consts (x) AS (VALUES (2)) INSERT INTO foo SELECT x FROM consts

即：WITH 子句创建一个派生表，然后您可以在主查询中使用该表；所以你实际上需要SELECT ... FROM 公用表表达式。