MySQL "ERROR 1046 (3D000): No database selected" on update query - php

Question

I have an UPDATE query where I explicitely reference the database, but MySQL still complains with the message: ERROR 1046 (3D000): No database selected.
Other queries that are similar of structure, but use an INSERT work fine. Other queries that only perform SELECTs also run fine.
To repeat the problem in a test case, try running these queries:
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();
Note: I'm running these queries from a PHP environment and I have NOT explicitely used mysql_select_db('test'), because I prefer not to and none of the other (many!) queries require it. I'm sure that using mysql_select_db would solve my issue, but I would like to know why exactly this particular query does not work.
For comparison sake: if you'd run this simpler query, also without using mysql_select_db, everything works fine:
update test.object1 set total=1, weight=1, dt=now() where id_object1=1;
I've searched to no avail. The only thing I found that came close, was this bug report: http://bugs.mysql.com/bug.php?id=28551 and especially that last (unanswered) message...

Answer 1

You have fields named incorrectly, but even if you correct them, this is a bug in MySQL that won't let you do it if you don't have default database.
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_object1, lur.id_object1, date(lur.dt)
order by
lur.id_object1, lur.id_object1
) 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();
The problem is specific to UPDATE with double-nested queries and no default database (SELECT or single-nested queries or default database work fine)

Answer 2

You have some wrong field names in the UPDATE statement -
What is s.object? Shouldn't it be s.id_object2?
What is lur.object1? Shouldn't it be lur.id_object1?
What is lur.object2? Shouldn't it be lur.id_object2?
What is ur.id_object at the end?
Fix all these issues and try to update again;-)
First time I ran this script I got that error. My output:
1 row inserted [0,184s]
1 row inserted [0,068s]
1 row inserted [0,066s]
1 row inserted [0,147s]
1 row inserted [0,060s]
Error (32,1): No database selected
When I set default database name the problem disappeared.

Answer 3

Remember that you cannot use foreign keys when the Engine is set to MyISAM. Not only does the table that you are creating a foreign key in need to be InnoDB, but the table you are getting the key from also needs to be InnoDB.
I was getting the same error as you and pulling my hair out for days before I thought of this. I went into each of my tables and made sure the Engines were set to InnoDB for each one, and now I have no issues setting up foreign keys.