test03=# insert into test values (1,'test',now()) on conflict (id) do update set info=excluded.info,crt_time=excluded.crt

PostgreSQL 9.5 引入了一项新功能，UPSERT(insert on conflict do)，当插入遇到约束错误时，直接返回，或者改为执行UPDATE。

语法如下

Command: INSERT
Description: create new rows in a table
Syntax:
[ WITH [ RECURSIVE ] with_query [, ...] ]
INSERT INTO table_name [ AS alias ] [ ( column_name [, ...] ) ]
{ 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 [, ...] ) = ( { expression | DEFAULT } [, ...] ) |  
                ( column_name [, ...] ) = ( sub-SELECT )  
              } [, ...]  
          [ WHERE condition ]

PostgreSQL 9.5以前的版本，可以通过函数，或者with语法来实现UPSERT类似的功能。

9.5+ UPSERT用法举例
创建一张测试表，其中一个字段为唯一键或者主键。

create table test(id int primary key, info text, crt_time timestamp);

不存在则插入，存在则更新

test03=# insert into test values (1,'test',now()) on conflict (id) do update set info=excluded.info,crt_time=excluded.crt_time;
INSERT 0 1

test03=# select * from test;
id | info | crt_time
----+------+----------------------------
1 | test | 2017-04-24 15:27:25.393948
(1 row)

test03=# insert into test values (1,'hello digoal',now()) on conflict (id) do update set info=excluded.info,crt_time=excluded.crt_time;
INSERT 0 1

test03=# select * from test;
id | info | crt_time
----+--------------+----------------------------
1 | hello digoal | 2017-04-24 15:27:39.140877
(1 row)

不存在则插入，存在则直接返回(不做任何处理)

test03=# insert into test values (1,'hello digoal',now()) on conflict (id) do nothing;
INSERT 0 0
test03=# insert into test values (1,'pu',now()) on conflict (id) do nothing;
INSERT 0 0
test03=# insert into test values (2,'pu',now()) on conflict (id) do nothing;
INSERT 0 1
test03=# select * from test;
id | info | crt_time
----+--------------+----------------------------
1 | hello digoal | 2017-04-24 15:27:39.140877
2 | pu | 2017-04-24 15:28:20.37392
(2 rows)
9.5- UPSERT用法举例
用户可以根据实际需求，使用不同的方法

函数

test03=# create or replace function f_upsert(int,text,timestamp) returns void as $$ declare res int; begin update test set info=$2,crt_time=$3 where id=$1; if not found then insert into test (id,info,crt_time) values ($1,$2,$3); end if; exception when others then return; end; $$ language plpgsql strict;
CREATE FUNCTION

test03=# select f_upsert(1,'digoal',now()::timestamp);

f_upsert

(1 row)

test03=# select f_upsert(1,'digoal001',now()::timestamp);

f_upsert

(1 row)

test03=# select f_upsert(3,'hello',now()::timestamp);

f_upsert

(1 row)

WITH语法，用法1

create table test(id int primary key, info text, crt_time timestamp);
存在则更新，不存在则插入。

with upsert as (update test set info=$info,crt_time=$crt_time where id=$id returning *) insert into test select $id,$info,$crt_time where not exists (select 1 from upsert where id=$id);
替换变量，进行测试

with upsert as (update test set info='test',crt_time=now() where id=1 returning *) insert into test select 1,'test',now() where not exists (select 1 from upsert where id=1);
同时插入一条不存在的值，只有一个会话成功，另一个会话会报PK约束错误。

WITH语法，用法2

即使表没有PK或者唯一约束，也能保证并发。

create table test(id int, info text, crt_time timestamp);
3.1 对于记录不存在，可以保证只有一个session插入数据，对于同一条数据更新，先来的session会lock着记录，后来的session会wait。

with
w1 as(select ('x'||substr(md5('$id'),1,16))::bit(64)::bigint as tra_id),
upsert as (update test set info=$info,crt_time=$crt_time where id=$id returning *)
insert into test select $id, $info, $crt_time from w1
where pg_try_advisory_xact_lock(tra_id) and not exists (select 1 from upsert where id=$id);
替换变量，进行测试

with
w1 as(select ('x'||substr(md5('1'),1,16))::bit(64)::bigint as tra_id),
upsert as (update test set info='digoal0123',crt_time=now() where id=1 returning *)
insert into test select 1, 'digoal0123', now() from w1
where pg_try_advisory_xact_lock(tra_id) and not exists (select 1 from upsert where id=1);

INSERT 0 0

with
w1 as(select ('x'||substr(md5('4'),1,16))::bit(64)::bigint as tra_id),
upsert as (update test set info='digoal0123',crt_time=now() where id=4 returning *)
insert into test select 4, 'digoal0123', now() from w1
where pg_try_advisory_xact_lock(tra_id) and not exists (select 1 from upsert where id=4);

INSERT 0 1

with w1 as(select ('x'||substr(md5('$id'),1,16))::bit(64)::bigint as tra_id),
upsert as (update test set info=$info,crt_time=$crt_time from w1 where pg_try_advisory_xact_lock(tra_id) and id=$id returning *)
insert into test select $id,$info,$crt_time from w1
where pg_try_advisory_xact_lock(tra_id) and not exists (select 1 from upsert where id=$id);
替换变量，进行测试

with w1 as(select ('x'||substr(md5('1'),1,16))::bit(64)::bigint as tra_id),
upsert as (update test set info='test',crt_time=now() from w1 where pg_try_advisory_xact_lock(tra_id) and id=1 returning *)
insert into test select 1,'test',now() from w1
where pg_try_advisory_xact_lock(tra_id) and not exists (select 1 from upsert where id=1);

INSERT 0 0

test03=# insert into test values (1,'test',now()) on conflict (id) do update set info=excluded.info,crt_time=excluded.crt_time; INSERT 0 1

f_upsert

f_upsert

f_upsert

NoSQL数据库

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