Postgres实现Merge

前言

Oracle迁移PG过程中遇到Merge语法的处理。PG 11开始支持Merge语法，但项目使用PG 10，所以要对代码中的Merge语句进行重写。

什么是Merge？

Oracle数据库MERGE语句_周末未至-CSDN博客_merge oracle

PG实现Merge的最佳实践

Best practices for migrating Oracle database MERGE statements to Amazon Aurora PostgreSQL and Amazon RDS PostgreSQL | AWS Database Blog

项目中Merge的情况比较简单，最后我采用了INSERT...ON CONFLICT...重写

如Oracle的Merge语句

MERGE INTO PRODUCT prd
USING PRODUCT_DELTA src
ON (prd.product_name = src.product_name 
    AND prd.product_type = src.product_type 
   )

WHEN MATCHED THEN
     UPDATE SET
         prd.unit_price = src.unit_price,
         modified_date  = SYSDATE

WHEN NOT MATCHED THEN
     INSERT(product_name, product_type, unit_price, modified_date)
     VALUES(src.product_name, src.product_type, src.unit_price, SYSDATE);

重写成Insert...on conflict...

INSERT INTO PRODUCT(product_name, product_type, unit_price, modified_date)
  SELECT   src.product_name,
         src.product_type,
         src.unit_price,
         now() modified_date
  FROM ( SELECT
         		product_name,
           	product_type,
           	unit_price
        	FROM PRODUCT_DELTA
  ) src

ON CONFLICT(product_name, product_type)

DO UPDATE
       SET
         unit_price   = excluded.unit_price,
         modified_date = excluded.modified_date;