Teradata Trigger Syntax (referencing similar rows for conditional insert) - sql

Question

I have a TeraData table that looks something like this:
Name;Year;Amount
1. Bob;2018;20
2. Bob;2022;14
3. Joe;2019;40
4. Ben;2017;12
The PK is Name and Year. I have a trigger in place that prevents a user from editing a row's Year to a lesser number. i.e. changing row 3 from 2019 to 2018.
That trigger is below:
Replace TRIGGER xyz.Month_Update
AFTER UPDATE OF Month ON xyz.table
REFERENCING OLD ROW as OldRow NEW ROW as NewRow
FOR EACH ROW
WHEN NewRow.Year < OldRow.Year
abort;
Now I would like to do something similar for insert.
I would like to prevent a user from inserting a new row into the table
if..
There already exists a row for the same person in the table and
That row(s) has a greater year than the one the user is attempting to enter
i.e. User can't enter Joe;2017;19 but user can enter Joe;2020;19
There are a few obvious problems with the trigger below but it shows the general idea:
Replace TRIGGER xyz.Month_Update
AFTER INSERT ON xyz.table
REFERENCING NEW ROW as NewRow
FOR EACH ROW
WHEN NewRow.Year < (select max(year) from xyz.table as t1 where t1.name = NewRow.name group by t1.name)
abort;
I'm new to triggers in general and teradata documentation appears porous.. any suggestions are greatly appreciated.

Answer 1

I don't know exactly if a Correlated Subquery like this is allowed in a Trigger (and how to write it correctly), but you can use Macros or Stored Procedures in a Trigger:
REPLACE MACRO xyz.Month_Insert_macro(yr INT, name VARCHAR(50)) AS
( ABORT 'Greater year already exists for that name'
WHERE :yr <
( SELECT Max(yr) FROM xyz.table
WHERE name= :name
);
);
Replace TRIGGER xyz.Month_Insert
-- it's better to abort BEFORE the Insert than AFTER (same for your Update Trigger)
BEFORE INSERT ON xyz.table
REFERENCING NEW ROW as NewRow
FOR EACH ROW
EXEC xyz.Month_Insert_macro(NewRow.yr, NewRow.name);