我有一个 UPDATE 查询,我在其中明确引用了数据库,但 MySQL 仍然抱怨消息:ERROR 1046 (3D000): No database selected
.
其他结构相似但使用 INSERT 的查询可以正常工作。仅执行 SELECT 的其他查询也可以正常运行。
要在测试用例中重复该问题,请尝试运行以下查询:
create table test.object1 (
id_object1 int unsigned not null auto_increment,
total int,
weight int,
dt datetime,
primary key (id_object1)
) engine=InnoDB;
create table test.object2 (
id_object2 int unsigned not null auto_increment,
primary key (id_object2)
) engine=InnoDB;
create table test.score (
id_object1 int unsigned not null,
id_object2 int unsigned not null,
dt datetime,
score float,
primary key (id_object1, id_object2),
constraint fk_object1 foreign key (id_object1) references object1 (id_object1),
constraint fk_object2 foreign key (id_object2) references object2 (id_object2)
) engine=InnoDB;
insert into test.object1 (id_object1, total, weight, dt) values (1, 0, 0, '2012-01-01 00:00:00');
insert into test.object1 (id_object1, total, weight, dt) values (2, 0, 0, '2012-01-02 00:00:00');
insert into test.object2 (id_object2) values (1);
insert into test.score (id_object1, id_object2, dt, score) values (1, 1, '2012-01-03 00:00:00', 10);
insert into test.score (id_object1, id_object2, dt, score) values (2, 1, '2012-01-04 00:00:00', 8);
update test.object1 p
join (
select ur.id_object1, sum(ur.score * ur.weight) as total, count(*) as weight
from (
select lur.*
from (
select s.id_object1, s.id_object2, s.dt, s.score, 1 as weight
from test.score as s
join test.object1 as o1 using(id_object1)
where s.dt > o1.dt
order by s.id_object1, s.id_object2, s.dt desc
) as lur
group by lur.id_object2, lur.id_object1, date(lur.dt)
order by lur.id_object1, lur.id_object2
) as ur
group by ur.id_object1
) as r using(id_object1)
set
p.total = p.total + r.total,
p.weight = p.weight + r.weight,
p.dt = now();
注意:我在 PHP 环境中运行这些查询,并且没有明确使用 mysql_select_db('test'),因为我不喜欢这样做,而且其他(很多!)查询都不需要它。我确信使用 mysql_select_db 会解决我的问题,但我想知道为什么这个特定的查询不起作用。
为了比较起见:如果您运行这个更简单的查询,也不使用 mysql_select_db,一切正常:
update test.object1 set total=1, weight=1, dt=now() where id_object1=1;
我已经搜索无济于事。我发现唯一接近的就是这个错误报告:http ://bugs.mysql.com/bug.php?id=28551 ,尤其是最后一条(未答复的)消息......