如果执行了 UPDATE，如何从“upsert”查询返回值？

Question

WITH upsert AS (UPDATE tbl SET a = 2 WHERE a = 1 RETURNING tbl.*)
INSERT INTO tbl (a)
SELECT 1 WHERE NOT EXISTS( SELECT * FROM upsert )
RETURNING *

这个“upsert”语句有效，但是我想检索 UPDATE 或 INSERTED 值。当 upsert 执行INSERT（行尚未在 db 中）时，插入的值将从查询中正确返回。

但是，当UPDATE执行时，不会返回任何值（但行是更新的）。我试过添加，RETURNING upsert.*但它产生错误missing FROM-clause entry for table \"upsert\"。

Answer 1

您需要为 INSERT 使用第二个 CTE：

WITH upsert AS (
  UPDATE tbl SET a = 2 
  WHERE a = 1 
  RETURNING tbl.*
), inserted AS (
  INSERT INTO tbl (a)
  SELECT 1 WHERE NOT EXISTS( SELECT * FROM upsert )
  RETURNING *
)
select *
from upsert
union all
select * 
from inserted