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：

[ 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;

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