CentOS

Hello,
In my web application based on Centos 6.7, there are querys generated by clients that stopped service mysqld that's why a message is shown "Database is not connected".
Please, is there any solution to know which query stopp the service mysqld.

You need to look at your logs and find out why it stops. It doesn't stop just because you run a query - it got an error of some kind or someone stopped it.

Wich log you want to look
Where is located ?

Start by reading /var/log/mysqld.log or /var/log/mariadb/mariadb.log, whichever version of "mysql" you are running. Also look in /var/log/messages for things like the linux Out Of Memory killer stepping in to save your whole system from dying.

Thanks for your response,
I don't have any error related to the service mysqld.
The only error shown in the file /var/log/message is below when the mysqld stop:

Mar 1 04:24:14 ******* dbus: [system] Rejected send message, 1 matched rules; type="method_call", sender=":1.202" (uid=0 pid=599 comm="/opt/teamviewer/tv_bin/TeamViewer_Desktop) interface="org.freedesktop.DBus.Properties" member="Get" error name="(unset)" requested_reply=0 destination="org.gnome.DisplayManager" (uid=0 pid=4114 comm="/usr/sbin/gdm-binary))

It seems related to teamviewer !
Can teamviewer influence in the CPU's use so that mysqld stops ??

That error is about a display problem, not anything to do with mysql at all. Look at your other log files too.

I've seen this kind of termination of the database server when the limit for max_allowed_packet in the server settings is to small.
This happens when a query references large objects in the database.
Like TrevorH said: look for error messages in your database server log files /var/log/mysqld.log or /var/log/mariadb/mariadb.log.