select host,name from hosts where hostid in (select hostid from items where itemid in (select itemid from trends_uint where itemid in (select itemid from items where name="Available memory") group by itemid having min(value_min)>2000000000));

出现10次以上，最大内存不足500MB的主机

select name from hosts where hostid in (select hostid from items where itemid in (select itemid from trends_uint where itemid in (select itemid from items where name="Available memory") and value_max<500000000 group by itemid having count(*)>10));