In the database table 'myprefix_sequence' I find the name 'myprefix_archive_numeric_2015_05' 113 times

This is problematic. The value should exist only once at all times. I can see there was a change recently
1238b6e @mattab .

If we do create a new sequence there, it should check for a specific exception, not just for any exception.

@msigrun Can you execute the following SQL query and post the output here? show create table myprefix_sequence; . In theory it should not be possible to have the same name there multiple times. Which MySQL version are you using?

It is MySQL 5

CREATE TABLE myprefix_sequence (
name varchar(120) CHARACTER SET utf8 NOT NULL,
value bigint(20) unsigned NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1

But this is strange: I am using Piwik also on a different server (same provider, also MySQL 5). There, Piwik 2.12.1 worked and I just succeeded with the update to 2.13.

Here is the SQL result:
CREATE TABLE piwik_sequence (
name varchar(120) NOT NULL,
value bigint(20) unsigned NOT NULL,
PRIMARY KEY (name)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

In the dumpfile of the elder database version it looks like this (from Piwik 2.12.1):
CREATE TABLE piwik_sequence (
name varchar(120) NOT NULL,
value bigint(20) unsigned NOT NULL,
PRIMARY KEY (name)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

How come that my other installation has PRIMARY KEY defined in table myprefix_sequence?

I tried this SQL-statement (with PRIMARY KEY) to solve the problem:
CREATE TABLE piwik_sequence (
name varchar(120) NOT NULL,
value bigint(20) unsigned NOT NULL,
PRIMARY KEY (name)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO myprefix_sequence (name, value) VALUES
('myprefix_archive_numeric_2015_04', 147),
('myprefix_archive_numeric_2015_03', 31),
('myprefix_archive_numeric_2015_02', 29),
('myprefix_archive_numeric_2015_01', 13),
('p1w1k82_archive_numeric_2015_05', 1);

Now, the data re-appeared. Fine.
But: under "Dashboard" there is written "Dashboard von myusername" - like always, but it is followed by: "Dashboard von myusername (2)" "Dashboard von myusername (3)" "Dashboard von myusername (4)" "Dashboard von myusername (5)"
(I use the German translation, "von" means "from" or "of")

I expected that for some random reason there's no primary key defined in your sequence table. There should a primary key defined (as you already figured out and added one). I have no clue how this can happen. Maybe someone else can? Do you use MySQL 5.0 or a later one?

The dashboard problem seems to be unrelated to this. At least I cannot explain how this could happen because of this. Is there maybe a primary key missing as well?

Can you execute the query show create table myprefix_user_dashboard

MySQL-Server is 5.5.41-0+wheezy1
and tadaaaaa:
CREATE TABLE myprefix_user_dashboard (
login varchar(100) CHARACTER SET utf8 NOT NULL,
iddashboard int(11) NOT NULL,
name varchar(100) CHARACTER SET utf8 DEFAULT NULL,
layout text CHARACTER SET utf8 NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1

whereas the other installation (which works) has
CREATE TABLE piwik_user_dashboard (
login varchar(100) NOT NULL,
iddashboard int(11) NOT NULL,
name varchar(100) DEFAULT NULL,
layout text NOT NULL,
PRIMARY KEY (login,iddashboard)
) ENGINE=MyISAM DEFAULT CHARSET=utf8

True. This table has no primary key and I am afraid more tables are affected. How come?

Should I contact my provider as both installations are a provided service (1st click installation)?

It would be great if you could contact your provider. Maybe they have heard of something like this before. It's the first time that I see such an issue. I have no clue how this can happen and didn't find anything when searching for it. Maybe someone else has an idea?

Thank you tsteur for your help. I will contact the provider and keep you informed.

Someone else has an idea? As this bug also existed somewhere else like in the forum I mentioned above.

I think the problem for the users in the forum was fixed. It was caused for them by a different problem.

The provider recommends a new installation. I will do this and then insert the existing data.

Thx for letting us know. I will close it for now. If anyone has an idea how this can happen, or whether it happened before (in this case we could maybe add a system check for this or a self-repair) please comment here.

@msigrun just a question, do you have another application installed in the same database?

No other application, I started with a new database.

I found the source of trouble when I did the new installation. In the beginning, the primary key was missing again, because I copied the original tables with a new prefix (phpMyAdmin 4.0.5).

If I do so, the copied table has no primary key! I tried this several times, every time it was like this. Just as I finally replaced the prefix piwik_ with myprefix_, the primary key stayed.

OK thx!