PostgreSQL 实现MySQL "insert ignore" 语法。

t_girl=# \d insert_ignore                         
           Table "ytt.insert_ignore"
  Column  |          Type          | Modifiers 
----------+------------------------+-----------
 id       | integer                | not null
 log_time | time without time zone | 
Indexes:
    "insert_ignore_pkey" PRIMARY KEY, btree (id)


t_girl=# select * from insert_ignore;
 id |    log_time    
----+----------------
  1 | 14:44:12.37185
(1 row)

第一种方法， 用自带的规则（RULE）来实现。

t_girl=# create rule r_insert_ignore as on insert to insert_ignore where exists (select 1 from insert_ignore where id = new.id) do instead nothing;    
CREATE RULE


这时，我们插入两条记录，其中一条的主键值已经存在，直接忽略掉。 实际插入的记录数为1.
t_girl=# insert into insert_ignore values(1,current_time),(2,current_time);
INSERT 0 1
t_girl=# select * from insert_ignore;
 id |    log_time     
----+-----------------
  1 | 14:44:12.37185
  2 | 14:48:22.222848
(2 rows)

t_girl=# create or replace function sp_insert_ignore() returns trigger as 
 $ytt$
 begin
   perform  1 from insert_ignore where id = new.id;
   if found then
     return null;
  end if;
  return new;
end;
$ytt$ language ‘plpgsql‘;
CREATE FUNCTION


对应的触发器如下：
t_girl=# create trigger tr_ib_insert_ignore before insert on insert_ignore for each row execute procedure sp_insert_ignore();
CREATE TRIGGER


继续插入两条记录。
t_girl=# insert into insert_ignore values (3,current_time),(2,current_time);
INSERT 0 1
t_girl=# select * from insert_ignore;
 id |    log_time     
----+-----------------
  1 | 14:44:12.37185
  2 | 14:48:22.222848
  3 | 15:05:33.198847
(3 rows)


OK。目的达到了。

t_girl=# insert into insert_ignore 
		with ytt_test(f1,f2) as (
							values(6,current_time),(3,current_time)
							) 
							select a.* from ytt_test as a where a.f1 not in (select id from insert_ignore as b);                          
INSERT 0 1
查看记录，插入了一条ID为6的记录，忽略了ID为3的记录。
t_girl=# select * from insert_ignore;
 id |    log_time     
----+-----------------
  1 | 14:44:12.37185
  2 | 14:48:22.222848
  3 | 15:05:33.198847
  6 | 15:15:52.297802
(4 rows)

t_girl=# create or replace function sp_insert_ignore (
IN f_id int,
IN f_log_time time without time zone
) returns void as 
$ytt$
begin
  insert into insert_ignore values (f_id,f_log_time);
  exception   when unique_violation  then
    raise notice ‘Duplicated Key Error on ID:%‘,f_id;
    return;
end;
$ytt$ language plpgsql;


第一次调用，抛出了错误。
t_girl=# select sp_insert_ignore(1,‘14:22:35‘::time); 
NOTICE:  Duplicated Key Error on ID:1
 sp_insert_ignore 
------------------
 
(1 row)


第二次正常插入。
t_girl=# select sp_insert_ignore(8,‘14:22:35‘::time);
 sp_insert_ignore 
------------------
 
(1 row)


t_girl=# select * from insert_ignore;
 id |    log_time     
----+-----------------
  1 | 14:44:12.37185
  2 | 14:48:22.222848
  3 | 15:05:33.198847
  6 | 15:15:52.297802
  8 | 14:22:35
(5 rows)


t_girl=# 

OK，目的也达到了。