如何仅更新 PostgreSQL 9.4 中另一个表的更改值？

Question

I have this query but updates the whole region_tmp table, which I dont want to, I only need to update a row in region table if anything has changed. I know I can specify which row with the regionid but am looking for something more general since I have a lot of records.

UPDATE REGION_TMP t SET
      REGIONID=R.REGIONID,
      REGIONDESCRIPTION=R.REGIONDESCRIPTION
FROM REGION R
WHERE R.REGIONID = T.REGIONID;

REGION TABLE:

REGIONID	REGIONDESCRIPTION
1	AMERICA
2	EUROPE
3	ASIA

REGION_TMP TABLE:

REGIONID	REGIONDESCRIPTION
1	AMERICA
2	EUROPE
3	AFRICA

My desire output in REGION_TMP:

REGIONID	REGIONDESCRIPTION
1	AMERICA
2	EUROPE
3	ASIA

Answer 1

My guess is that you need to create a duplicate of your REGION table, but you already have a REGION_TMP table, so you just want to update the values that do not match.

In order to achieve that, you need to join the two tables inside the UPDATE statement and replace the values of REGION_TMP.REGIONDESCRIPTION with the corresponding REGION.REGIONDESCRIPTION where the REGION_ID applies for both and the REGIONDESCRIPTION is different:

UPDATE REGION_TMP
SET REGIONDESCRIPTION = REGION.REGIONDESCRIPTION
FROM REGION
WHERE REGION_TMP.REGIONID = REGION.REGIONID
  AND REGION_TMP.REGIONDESCRIPTION <> REGION.REGIONDESCRIPTION;

Check the demo here .