sql - 发生冲突的 Postgres 会更新复合主键

Question

我有一张表格，用户可以在其中回答问题。规则是用户可以回答许多问题，或者许多用户可以回答一个问题，但一个用户只能回答一个特定问题一次。如果用户再次回答这个问题，它应该简单地替换旧的。通常，当我们处理唯一列时，on conflict do update 起作用。在这种情况下，列 person_id 和 question_id 不能是唯一的。然而，两者的结合总是独一无二的。如何实现在冲突时更新的插入语句？

CREATE TABLE "answer" (
  "person_id" integer NOT NULL REFERENCES person(id), 
  "question_id" integer NOT NULL REFERENCES question(id) ON DELETE CASCADE, /* INDEXED */
  "answer" character varying (1200) NULL,
  PRIMARY KEY (person_id, question_id) 
);

Answer 1

只需将两个键都放在 ON CONFLICT 中子句:

INSERT INTO answer VALUES (1,1,'q1') 
ON CONFLICT (person_id,question_id) 
DO UPDATE SET answer = EXCLUDED.answer; 

例子:

INSERT INTO answer VALUES (1,1,'q1') 
ON CONFLICT (person_id,question_id) 
DO UPDATE SET answer = EXCLUDED.answer;             

SELECT * FROM answer;
 person_id | question_id | answer 
-----------+-------------+--------
         1 |           1 | q1
(1 Zeile)

INSERT INTO answer VALUES (1,1,'q1') 
ON CONFLICT (person_id,question_id) 
DO UPDATE SET answer = EXCLUDED.answer || '-UPDATED';             

SELECT * FROM answer;
 person_id | question_id |   answer   
-----------+-------------+------------
         1 |           1 | q1-UPDATED
(1 Zeile)

演示: db<>fiddle

PostgreSQL 15 +

您也可以使用 MERGE 获得相同的结果:

MERGE INTO answer i
  -- records to be inserted
  USING (
    VALUES (1,1,'q1'), -- already exists in table answers!
           (2,2,'q2')  -- new record
  ) AS j (person_id, question_id, answer)
  -- checking if the PK of given records (j) already exists
  -- in table "answer" (i).
  ON j.question_id = i.question_id AND j.person_id = i.person_id
WHEN MATCHED THEN
  -- in case of a match (conflict), I want to add the suffix '-UPDATED' 
  -- to the column "answer"
  UPDATE SET answer = j.answer || '-UPDATED'
WHEN NOT MATCHED THEN 
  -- if there is no match (conflict) just INSERT the record.
  INSERT (person_id, question_id, answer)
  VALUES (j.person_id, j.question_id, j.answer);

演示: db<>fiddle