Brian is correct that there's no direct way of doing this. You will need to add another field to capture an additional data point whenever you have a duplicate 'task_sla' record entered. Then you can easily filter what you want on this entry. Here's how you can accomplish this.
1) Create a new 'True/False' field on the 'task_sla' table named 'Last added (u_last_added)'. Give it a default value of 'true'. This field will only be updated by the system so you can also mark it as 'Read only' in the dictionary. This is the field you'll be able to filter on to only show the latest SLA per type. You'll be able to filter and show 'task_sla' records where this field is 'true'.
2) Create a new business rule on the 'task_sla' table with the following settings...
Name: Update 'Last added' SLA
When: After
Insert: True
Advanced: True
Condition: !current.task.nil() && !current.sla.nil()
Script:
(function executeRule(current, previous /*null when async*/) {
// Find the 'Last added' SLA for this task/sla combination and mark it
var tsla = new GlideRecord('task_sla');
tsla.addQuery('task', current.task);
tsla.addQuery('sla', current.sla);
tsla.addQuery('u_last_added', true);
tsla.addQuery('sys_id', '!=', current.sys_id);
tsla.query();
if (tsla.next()) {
tsla.u_last_added = false; // Change the 'u_last_added' field to 'false'
tsla.autoSysFields(false); // Don't update time stamps
tsla.setWorkflow(false); // Don't run any business rules
tsla.update();
}
})(current, previous);
3) The above will solve the problem for SLAs added in the future, but you will also need to run a one-time background script to update any existing data. You can run the following script from the 'Scripts -> Background' module. You'll be updating every 'task_sla' record in your system (no business rules or time stamps will be applied) so proceed with caution and test thoroughly!
var lastTask = '';
var lastsla = '';
// Query all 'task_sla' records
var allsla = new GlideRecord('task_sla');
// Order by task and sla, then by 'sys_created_on' to group correctly
allsla.orderBy('task');
allsla.orderBy('sla');
allsla.orderByDesc('sys_created_on');
allsla.query();
while (allsla.next()) {
allsla.u_last_added = false;
// Find the 'Last added' SLA for this task/sla combination and mark it
if ((allsla.task != lastTask) || (allsla.sla != lastsla)) {
lastTask = allsla.task.toString();
lastsla = allsla.sla.toString();
allsla.u_last_added = true; // Change the 'u_last_added' field to 'true'
}
allsla.autoSysFields(false); // Don't update time stamps
allsla.setWorkflow(false); // Don't run any business rules
allsla.update();
}
