PostgreSQL的upsert实例操作(insert on conflict do)
建表语句：
DROP TABLE IF EXISTS “goods”;
CREATE TABLE “goods” (
“store_cd” int4 NOT NULL,
“good_cd” varchar(50) COLLATE “pg_catalog”.”default” NOT NULL,
“name” varchar(255) COLLATE “pg_catalog”.”default”
);
INSERT INTO “goods” VALUES (101, ‘1’, ‘张三’);
INSERT INTO “goods” VALUES (102, ‘2’, ‘李四’);
INSERT INTO “goods” VALUES (103, ‘3’, ‘王五’);
ALTER TABLE “goods” ADD CONSTRAINT “pr_cd_key” PRIMARY KEY (“store_cd”, “good_cd”);
表数据：
数据存在则更新数据，不存在则插入数据
INSERT INTO GOODS VALUES ( 104, ‘4’, ‘赵六’ )
ON CONFLICT ON CONSTRAINT pr_key_cd DO
UPDATE
SET NAME = ‘更新’
WHERE
GOODS.STORE_CD = ‘104’
AND GOODS.GOOD_CD = ‘4’
pr_key_cd为必须为唯一主键，也可以用下面写法（注意：必须保证筛选出数据唯一）
INSERT INTO GOODS VALUES ( 104, ‘4’, ‘赵六’ )
ON CONFLICT ( STORE_CD, GOOD_CD ) DO
UPDATE
SET NAME = ‘更新’
WHERE
GOODS.STORE_CD = ‘104’
AND GOODS.GOOD_CD = ‘4’
上面的两种的写法，是先执行insert如果主键冲突则执行update，没有冲突就执行insert了。要是想先执行update语句呢？
update更新失败执行insert，更新成功则执行update。
WITH TABLE1 AS ( UPDATE GOODS SET NAME = ‘更新’ WHERE STORE_CD = ‘104’ AND GOOD_CD = ‘4’ RETURNING * )
INSERT INTO GOODS SELECT 104, ‘4’, ‘赵六’
WHERE NOT EXISTS ( SELECT 1 FROM TABLE1 WHERE STORE_CD = ‘104’ AND GOOD_CD = ‘4’ )
补充：Postgresql插入或更新操作upsert
幂等性的一个要求是多次操作的结果一致。对于update操作，多次直接的结果都是最后update的值，是满足需求的。但对于insert，如果已经插入，第二次会报错，duplicate error， 主键重复或者unique key duplicate。所以需要做一下处理。
最简单的就是，try-catch，当报错的时候，调用update去更新，或者策略更简单点，直接返回就行，不需要更新，以第一条为准。
PostgreSQL从9.5之后就提供了原子的upsert语法： 不存在则插入，发生冲突可以update。
Inert语法
官方文档： https://www.postgresql.org/docs/devel/sql-insert.html
[ WITH [ RECURSIVE ] with_query [, …] ]
INSERT INTO table_name [ AS alias ] [ ( column_name [, …] ) ]
[ OVERRIDING { SYSTEM | USER} VALUE ]
{ DEFAULT VALUES | VALUES ( { expression | DEFAULT } [, …] ) [, …] | query }
[ ON CONFLICT [ conflict_target ] conflict_action ]
[ RETURNING * | output_expression [ [ AS ] output_name ] [, …] ]
where conflict_target can be one of:
( { index_column_name | ( index_expression ) } [ COLLATE collation ] [ opclass ] [, …] ) [ WHERE index_predicate ]
ON CONSTRAINT constraint_name
and conflict_action is one of:
DO NOTHING
DO UPDATE SET { column_name = { expression | DEFAULT } |
( column_name [, …] ) = [ ROW ] ( { expression | DEFAULT } [, …] ) |
( column_name [, …] ) = ( sub-SELECT )
} [, …]
[ WHERE condition ]
index_column_name
The name of a table_name column. Used to infer arbiter indexes. Follows CREATE INDEX format. SELECT privilege on index_column_name is required.
index_expression
Similar to index_column_name, but used to infer expressions on table_name columns appearing within index definitions (not simple columns). Follows CREATE INDEX format. SELECT privilege on any column appearing within index_expression is required.
使用示例
创建表
CREATE TABLE “test”.”upsert_test” (
“id” int4 NOT NULL,
“name” varchar(255) COLLATE “pg_catalog”.”default”
)
;
当主键id冲突时，更新其他字段
INSERT INTO test.upsert_test(id, “name”)
VALUES(1, ‘m’),(2, ‘n’),(4, ‘c’)
ON conflict(id) DO UPDATE
SET “name” = excluded.name;
did 冲突的主键
EXCLUDED 代指要插入的记录
当主键或者unique key发生冲突时，什么都不做
INSERT INTO test.upsert_test(id, “name”)
VALUES(1, ‘m’),(2, ‘n’),(4, ‘c’)
ON conflict(id) DO NOTHING;
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。如有错误或未考虑完全的地方，望不吝赐教。
