https://yq.aliyun.com/articles/74419

原址

標籤

PostgreSQL , upsert , insert on conflict do

---

背景

PostgreSQL 9.5 引入了一項新功能，UPSERT(insert on conflict do)，當插入遇到約束錯誤時，直接返回，或者改爲執行UPDATE。

語法如下

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，可以通過函數，或者with語法來實現UPSERT類似的功能。

9.5+ UPSERT用法舉例

創建一張測試表，其中一個字段爲唯一鍵或者主鍵。

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

1. 不存在則插入，存在則更新

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)  

2. 不存在則插入，存在則直接返回(不做任何處理)

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用法舉例

用戶可以根據實際需求，使用不同的方法

1. 函數

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

CREATE FUNCTION  

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

f_upsert

(1 row)

test03=# select * from test;
id | info | crt_time
—-+——–+—————————-
2 | pu | 2017-04-24 15:28:20.37392
1 | digoal | 2017-04-24 15:31:29.254325
(2 rows)

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

f_upsert

(1 row)

test03=# select * from test;
id | info | crt_time
—-+———–+—————————
2 | pu | 2017-04-24 15:28:20.37392
1 | digoal001 | 2017-04-24 15:31:38.0529
(2 rows)

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

f_upsert

(1 row)

test03=# select * from test;
id | info | crt_time
—-+———–+—————————
2 | pu | 2017-04-24 15:28:20.37392
1 | digoal001 | 2017-04-24 15:31:38.0529
3 | hello | 2017-04-24 15:31:49.14291
(3 rows)

2. WITH語法，用法1

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

存在則更新，不存在則插入。

with upsert as (update test set info=$info,crt_time=$crt_time where id=$<span class="hljs-keyword">id</span> <span class="hljs-keyword">returning</span> *) <span class="hljs-keyword">insert</span> <span class="hljs-keyword">into</span> <span class="hljs-keyword">test</span> <span class="hljs-keyword">select</span> $id,$info,$crt_time where not exists (select 1 from upsert where id=$id);    

替換變量，進行測試

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);    

同時插入一條不存在的值，只有一個會話成功，另一個會話會報PK約束錯誤。

3. WITH語法，用法2

即使表沒有PK或者唯一約束，也能保證併發。

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

3.1 對於記錄不存在，可以保證只有一個session插入數據，對於同一條數據更新，先來的session會lock着記錄，後來的session會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 $<span class="hljs-keyword">id</span>, $info, $crt_time from w1     
    where pg_try_advisory_xact_lock(tra_id) and not exists (select 1 from upsert where id=$id);    

替換變量，進行測試

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  

test03=# select * from test;  
 id |    info    |         crt_time            
----+------------+---------------------------  
  2 | pu         | 2017-04-24 15:28:20.37392  
  3 | hello      | 2017-04-24 15:31:49.14291  
  1 | digoal0123 | 2017-04-24 15:31:38.0529  
(3 rows)  

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  

test03=# select * from test;  
 id |    info    |          crt_time            
----+------------+----------------------------  
  2 | pu         | 2017-04-24 15:28:20.37392  
  3 | hello      | 2017-04-24 15:31:49.14291  
  1 | digoal0123 | 2017-04-24 15:31:38.0529  
  4 | digoal0123 | 2017-04-24 15:38:39.801908  
(4 rows)  

3.2 對於記錄不存在，可以保證只有一個session插入數據，對於同一條數據更新，先來的session會更新數據，後來的session不等待，直接失敗。

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 $<span class="hljs-keyword">id</span>,$info,$crt_time from w1   
    where pg_try_advisory_xact_lock(tra_id) and not exists (select 1 from upsert where id=$id);     

替換變量，進行測試

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=# select * from test;  
 id |    info    |          crt_time            
----+------------+----------------------------  
  2 | pu         | 2017-04-24 15:28:20.37392  
  3 | hello      | 2017-04-24 15:31:49.14291  
  4 | digoal0123 | 2017-04-24 15:42:50.912887  
  1 | test       | 2017-04-24 15:44:44.245167  
(4 rows)