PostgreSQL忘记输入where条件update更新整张表的解决办法

虽然出现这个错误很挫，但有时候还是会被你或者你的同事碰到。为了避免这个错误，PostgreSQL数据库中可以通过触发器来解决，这里用的是plpgsql 。

1、修改postgresql.conf配置

增加：custom_variable_classes = 'limits'
重新加载：pg_ctl reload

2、创建触发器函数

CREATE OR REPLACE FUNCTION zero_counter()
 RETURNS TRIGGER
 LANGUAGE plpgsql
 AS
$BODY$
DECLARE
BEGIN
 PERFORM set_config('limits.test', '0', true);
 IF TG_OP = 'UPDATE' THEN
 RETURN NEW;
 END IF;
 RETURN OLD;
END;
$BODY$;

CREATE OR REPLACE FUNCTION limit_modifications()
 RETURNS TRIGGER
 LANGUAGE plpgsql
 AS
$BODY$
DECLARE
 i INT4;
BEGIN
 i := current_setting('limits.test')::INT4 + 1;
 PERFORM set_config('limits.test', i::TEXT, true);
 IF i > 5000 THEN
 RAISE EXCEPTION '% of more than 5000 row is forbidden.', TG_OP;
 END IF;
 IF TG_OP = 'UPDATE' THEN
 RETURN NEW;
 END IF;
 RETURN OLD;
END;
$BODY$;

3、测试

forummon=# create table test as select i as id, 'password for: ' || i as pass from generate_series(1,10000) i;
forummon=# CREATE TRIGGER zero_counter BEFORE UPDATE OR DELETE ON test FOR EACH STATEMENT EXECUTE PROCEDURE zero_counter();
CREATE TRIGGER
forummon=# CREATE TRIGGER limit_modifications BEFORE UPDATE OR DELETE ON test FOR EACH ROW EXECUTE PROCEDURE limit_modifications();
CREATE TRIGGER
forummon=# \d+ test 
 Table "public.test"
 Column | Type | Modifiers | Storage | Stats target | Description 
--------+---------+-----------+----------+--------------+-------------
 id | integer | | plain | | 
 pass | text | | extended | | 
Triggers:
 limit_modifications BEFORE DELETE OR UPDATE ON test FOR EACH ROW EXECUTE PROCEDURE limit_modifications()
 zero_counter BEFORE DELETE OR UPDATE ON test FOR EACH STATEMENT EXECUTE PROCEDURE zero_counter()
Has OIDs: no

forummon=# update test set pass = 'qq' where id<5003 ;
ERROR: UPDATE of more than 5000 row is forbidden.
forummon=# update test set pass = 'qq' where id<5000 ;
UPDATE 4999
forummon=# drop table test ;
DROP TABLE

总结

批量操作的数量限制可以在limit_modifications中修改，切记在update不确定时先select再update。

参考连接：http://www.depesz.com/2007/07/27/update-account-set-password-new_password-oops/

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