在postgres上使用什么代替“ INSERT ... ON CONFLICT DO NOTHING”

Question

我有以下查询，与postgres 9.5一起使用：

INSERT INTO knowledge_state 
(SELECT learnerid learner_id, lo_id FROM qb_lo_tag WHERE qb_id = NEW.qb_id)
ON CONFLICT DO NOTHING ;

不幸的是，我不能在某些服务器上使用postgres 9.5，我需要将其转换为9.5之前的友好查询。我建立了以下查询，但对我来说似乎复杂得多，我认为可能有更简单的方法。

FOR rows IN SELECT lo_id FROM knowledge_state 
WHERE learner_id = learnerid 
AND lo_id IN (SELECT lo_id FROM qb_lo_tags WHERE qb_id = New.qb_id) LOOP

  INSERT INTO knowledge_state (lo_id, learner_id) SELECT rows.lo_id, learnerid 
WHERE NOT EXISTS (SELECT * FROM knowledge_state WHERE lo_id = rows.lo_id AND learner_id = learnerid);

END LOOP;

我很想听听有关如何简化此查询的想法。

Answer 1

只要做你正在做的事情，没有循环：

INSERT INTO knowledge_state (lo_id, learner_id) 
SELECT  a.lo_id, a.learnerid
FROM qb_lo_tag a
WHERE a.qb_id = NEW.qb_id
and  NOT EXISTS (SELECT * FROM knowledge_state b 
     WHERE b.lo_id = a.lo_id AND b.learner_id = a.learnerid);

当然，你可以在knowledge_state(lo_id, learner_id)上添加索引，以使其更快（On Conflict意味着唯一约束或其他约束，唯一约束意味着索引）。