Best Practices

This select statement is from my rule which sends this notification in our environment.

select HD_TICKET.*, DATE_FORMAT(HD_TICKET.CREATED,'%b %d %Y %I:%i:%s %p') as CREATED, DATE_FORMAT(HD_TICKET.MODIFIED,'%b %d %Y %I:%i:%s %p') as MODIFIED,
                        HD_STATUS.NAME AS STATUS_NAME,
                        HD_STATUS.ORDINAL as STATUS_ORDINAL,
                        HD_IMPACT.ORDINAL as IMPACT_ORDINAL,
                        HD_CATEGORY.ORDINAL as CATEGORY_ORDINAL,
                        HD_PRIORITY.ORDINAL as PRIORITY_NUMBER,
                        STATE, 
                        if((datediff(DUE_DATE, now()) = 0), 2, if((datediff(DUE_DATE, now())<0), 1, 3)) as SORT_OVERDUE_STATUS,
                        if(unix_timestamp(TIME_OPENED) > 0, TIME_OPENED, 1<<62) as SORT_TIME_OPENED, 
                        if(unix_timestamp(TIME_STALLED) > 0, TIME_STALLED, 1<<62) as SORT_TIME_STALLED, 
                        if(unix_timestamp(TIME_CLOSED) > 0, TIME_CLOSED, 1<<62) as SORT_TIME_CLOSED, 
                        if(unix_timestamp(ESCALATED) > 0, ESCALATED, 1<<62) as SORT_ESCALATED,
                        if(unix_timestamp(HD_TICKET.CREATED) > 0, HD_TICKET.CREATED, 1<<62) as SORT_TIME_CREATED, 
                        if(unix_timestamp(HD_TICKET.MODIFIED) > 0, HD_TICKET.MODIFIED, 1<<62) as SORT_MODIFIED,
                        if(unix_timestamp(HD_TICKET.DUE_DATE) > 0, HD_TICKET.DUE_DATE, 1<<62) as SORT_DUE_DATE,
                        case upper(STATE) 
                        when 'CLOSED' then unix_timestamp(HD_TICKET.TIME_CLOSED) - unix_timestamp(HD_TICKET.TIME_OPENED) 
                        when 'OPENED' then unix_timestamp(NOW()) - unix_timestamp(HD_TICKET.TIME_OPENED) 
                        else unix_timestamp(NOW()) - unix_timestamp(HD_TICKET.CREATED) end as AGE,
                        if ((LENGTH(U1.FULL_NAME) = 0), U1.USER_NAME, U1.FULL_NAME) as OWNER_NAME,
                        U1.FULL_NAME as OWNER_FULLNAME,
                        U1.EMAIL as OWNER_EMAIL,
                        if (U1.ID is null, 'z', concat('a', if ((LENGTH(U1.FULL_NAME) = 0), U1.USER_NAME, U1.FULL_NAME))) as SORT_OWNER_NAME,
                        if ((LENGTH(U2.FULL_NAME) = 0), U2.USER_NAME, U2.FULL_NAME) as SUBMITTER_NAME,
                        U2.FULL_NAME as SUBMITTER_FULLNAME,
                        U2.EMAIL as SUBMITTER_EMAIL,
                        if (U2.ID is null, 'z', concat('a', if ((LENGTH(U2.FULL_NAME) = 0), U2.USER_NAME, U2.FULL_NAME))) as SORT_SUBMITTER_NAME,
                        if (U3.ID is null, 'z', concat('a', if ((LENGTH(U3.FULL_NAME) = 0), U3.USER_NAME, U3.FULL_NAME))) as SORT_APPROVER_NAME,
                        if(APPROVAL='rejected', 'Rejected', if(APPROVAL='info', 'More Info Needed', if(APPROVAL='approved', 'Approved', if(APPROVER_ID>0, 'Pending', '')))) as APPROVAL_STATUS,
                        Q.NAME as QUEUE_NAME,
U4.EMAIL as PREVIOUS_OWNER_EMAIL,
U5.EMAIL as NEW_OWNER_EMAIL               
                        from (HD_TICKET, HD_PRIORITY, HD_STATUS, HD_IMPACT, HD_CATEGORY)
JOIN HD_TICKET_CHANGE ON HD_TICKET_CHANGE.HD_TICKET_ID = HD_TICKET.ID 
 and HD_TICKET_CHANGE.ID=<CHANGE_ID>
JOIN HD_TICKET_CHANGE_FIELD ON HD_TICKET_CHANGE_FIELD.HD_TICKET_CHANGE_ID=<CHANGE_ID>
 and HD_TICKET_CHANGE_FIELD.FIELD_CHANGED='OWNER_ID'
                        LEFT JOIN USER U1 on U1.ID = HD_TICKET.OWNER_ID
                        LEFT JOIN USER U2 on U2.ID = HD_TICKET.SUBMITTER_ID
                        LEFT JOIN USER U3 on U3.ID = HD_TICKET.APPROVER_ID
LEFT JOIN USER U4 on U4.ID = HD_TICKET_CHANGE_FIELD.BEFORE_VALUE
LEFT JOIN USER U5 on U5.ID = HD_TICKET_CHANGE_FIELD.AFTER_VALUE
                        LEFT JOIN HD_QUEUE Q on Q.ID = HD_TICKET.HD_QUEUE_ID
                        LEFT JOIN MACHINE M1 on M1.ID = HD_TICKET.MACHINE_ID
                        where HD_PRIORITY.ID = HD_PRIORITY_ID
                        and HD_STATUS.ID = HD_STATUS_ID
                        and HD_IMPACT.ID = HD_IMPACT_ID
                        and HD_CATEGORY.ID = HD_CATEGORY_ID
                        and ((  (1  in (select 1 from HD_TICKET_CHANGE where HD_TICKET_CHANGE.HD_TICKET_ID = HD_TICKET.ID)) ) and HD_TICKET_CHANGE.USER_ID != U4.ID)

This query uses the data in the HD_TICKET_CHANGE_FIELD table for the current change ID when the changed field is the OWNER_ID. It will also only trigger if the user that made the change to the ticket is not the previous owner, i.e. if I transfer one of my own tickets to someone else, I won't get the notification that it was transferred. 

The Column containing email addresses is PREVIOUS_OWNER_EMAIL.