in this case for zabbix database:
Convert tables from latin1 to utf-8 :
mysql zabbix -B -N -e 'show tables' | xargs -L 1 | awk '{print "ALTER TABLE "$1" CONVERT TO CHARACTER SET utf8 COLLATE utf8_bin"}' | xargs -L 1 -I {} echo mysql zabbix -e \' {} \' | sh -x
convert database charset :
mysql -e 'ALTER DATABASE zabbix DEFAULT CHARACTER SET utf8 COLLATE utf8_bin'