SELECT CONVERT_TZ(displaytime,'GMT','MET');
should work if your column type is timestamp, or date
Test how this works:
SELECT CONVERT_TZ(a_ad_display.displaytime,'+00:00','+04:00');Check your timezone-table
SELECT * FROM mysql.time_zone;
SELECT * FROM mysql.time_zone_name;If those tables are empty, you have not initialized your timezone tables. According to link above you can use mysql_tzinfo_to_sql program to load the Time Zone Tables. Please try this
shell> mysql_tzinfo_to_sql /usr/share/zoneinfo