PostgreSQL upset解決在插入過程中重復數據沖突

關於重復行問題：

　　在SQL Server中則可以自動排出重復行，不需要處理。在Oracle中經常遇到upsert語法，來排出沖突行。在PostgreSQL中，也需要手動排出重復行，否則會爆出錯誤，upsert用法如下：

　　

    WITH upsert AS (
         UPDATE TEST AS a
         SET
         updatetime=b.updatetime, msec=b.msec
         FROM TEMP_WRITEEVTUPDATETMSTAMP AS b
         WHERE a.deviceid=b.deviceid AND a.eventtype=b.eventtype
         RETURNING a.deviceid,a.eventtype

     )
     INSERT INTO TEST
     SELECT b.deviceid, b.eventtype, b.updatetime,b.msec
     FROM TEMP_WRITEEVTUPDATETMSTAMP b
     WHERE NOT EXISTS (SELECT 1 FROM upsert as a WHERE a.deviceid=b.deviceid AND a.eventtype=b.eventtype);    

 

　　經過測試，發現這種方法效率很低，於是將upsert過程拆分為兩個過程，先insert不重復的數據，然后再執行update：

　　

    INSERT INTO TEST
     Select b.*
     from TEMP_WRITEEVTUPDATETMSTAMP b, (select deviceid, eventtype, max(ctid) max_ctid from TEMP_WRITEEVTUPDATETMSTAMP group by deviceid, eventtype) c
     where (b.deviceid = c.deviceid and b.eventtype = c.eventtype and b.ctid = c.max_ctid) and NOT EXISTS (SELECT 1 FROM TEST as a WHERE a.deviceid=b.deviceid AND a.eventtype=b.even

     UPDATE TEST AS a
     SET
     updatetime=b.updatetime, msec=b.msec
     FROM TEMP_WRITEEVTUPDATETMSTAMP AS b
     WHERE a.deviceid=b.deviceid AND a.eventtype=b.eventtype;

 

當時在存儲過程中大量使用該方法來去除重復數據的插入，但是最后發現還有更好的方法來處理，upsert：

　　　INSERT INTO TEST
     select * from TEMP_WRITEEVTUPDATETMSTAMP on conflict pk_test_deviceid_eventtype do update set updatetime = excluded.updatetime, msec = excluded.msec;