PostgreSQL实现MySQL"insertignore"_MySQL

bitsCN.com 对MySQL熟悉的人可能都知道，MySQL 有一个“insert ignore" 语法来忽略已经存在的记录。 PostgreSQL暂时不提供这样的语法，但是可以用其他方法来代替。
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)

我来演示下几种代替方法。<strong>第一种方法， 用自带的规则（RULE）来实现。</strong> 

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)

第二种方法， 建立一个返回NULL的触发器函数。 那么函数体如下： 

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 1t_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。 

<strong>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)</strong><strong>第四种，用存储过程来代替INSERT处理。</strong>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 &#39;Duplicated Key Error on ID:%&#39;,f_id; return; end; $ytt$ language plpgsql; 第一次调用，抛出了错误。 t_girl=# select sp_insert_ignore(1,&#39;14:22:35&#39;::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,&#39;14:22:35&#39;::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。

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