soft delete on update in mysql with multiple schemas - mysql

Question

I am in this situation:
Background
I have 2 database schemas called "prod" and "stg".
"prod" contains 2 tables called "parent" and "child"
"stg" only has the "parent" table
"parent" table defination is the same across "prod" and "stg" schemas.
In the case of deleting records, "parent" table is defined as soft delete (logically deletion, i.e. set delete_flg as "1") whereas the "child" table is true delete (physically remove the record)
Goal
I am trying to achieve the following goal:
when and only when both "prod"."parent" and "stg"."parent" are deleted (no matter physically or logically, or does not exist on one side) then automatically cascade a delete operation(physically remove) to the record in "prod"."child" table whose "SP_ID" matches the value in "parent".
For example, assuming I have
"prod"."parent"
+----+---------+--------+
| SP_ID | SP_NAME | DELETE_FLG |
+----+---------+--------+
| 1 | 1 | 1 |
+----+---------+--------+
"prod"."parent"
+----+---------+--------+
| SP_ID | SP_NAME | DELETE_FLG |
+----+---------+--------+
| 1 | 1 | 1 |
+----+---------+--------+
"stg"."parent"
+----+---------+--------+
| SP_ID | SP_NAME | DELETE_FLG |
+----+---------+--------+
| 1 | 1 | 0 |
+----+---------+--------+
"prod"."child"
+----+---------+
| SP_ID | JOB_KEY |
+----+---------+
| 1 | key |
+----+---------+
, if I execute a sql update "stg"."parent" set DELETE_FLG = 1 where SP_ID = 1, which logically delete the last "existing" record in "parent" table that has SP_ID 1, then the record in "prod"."child" will also be automatically phycially deleted by mysql.
Question
I have been thinking about making the SP_ID in the child table as a foreign key referencing the one in parent able (https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html)
however,
a) I don't know whether it is possible to reference multiple tables in differnet schemas, and
b) It seems mysql only support cascading same operation, i.e. delete on parent then delete the child OR update on parent then update the child. But in my case, I want a update on parent then delete the child.
Could somebody help me out here please?
Is this possible to be achieved in mysql? or I have to do this in application layer?
Table definition
CREATE TABLE `prod`.`parent` (
`SP_ID` varchar(20) NOT NULL COMMENT '',
`SP_NAME` varchar(100) NOT NULL COMMENT '',
`DELETE_FLG` tinyint(1) NOT NULL DEFAULT '0' COMMENT '',
PRIMARY KEY (`SP_ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT=''
CREATE TABLE `prod`.`child` (
`SP_ID` varchar(20) NOT NULL COMMENT '',
`JOB_KEY` varchar(11) NOT NULL,
PRIMARY KEY (`SP_ID`,`JOB_KEY`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT=''
CREATE TABLE `stg`.`parent` (
`SP_ID` varchar(20) NOT NULL COMMENT '',
`SP_NAME` varchar(100) NOT NULL COMMENT '',
`DELETE_FLG` tinyint(1) NOT NULL DEFAULT '0' COMMENT '',
PRIMARY KEY (`SP_ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT=''

Answer 1

with the hint of using triggers, This is my solution which works:
Add 2 triggers(one is after update, on is after delete) to both prod and stg parent tables.
# after update trigger
CREATE DEFINER=`root`#`localhost` TRIGGER `stg`.`parent_AFTER_UPDATE` AFTER UPDATE ON `parent` FOR EACH ROW
BEGIN
IF (
select
count(*)
from(
select
*
from `prod`.`parent`
where `prod`.`parent`.id = old.id and `prod`.`parent`.delete_flg = 0
Union all
select
*
from `stg`.`parent`
where `stg`.`parent`.id = old.id and `stg`.`parent`.delete_flg = 0
) as a
) = 0 THEN
DELETE FROM `prod`.`child` WHERE `prod`.`child`.id = old.id;
END IF;
END
# after delete trigger
CREATE DEFINER=`root`#`localhost` TRIGGER `stg`.`parent_AFTER_DELETE` AFTER DELETE ON `parent` FOR EACH ROW
BEGIN
IF (
select
count(*)
from(
select
*
from `prod`.`parent`
where `prod`.`parent`.id = old.id and `prod`.`parent`.delete_flg = 0
Union all
select
*
from `stg`.`parent`
where `stg`.`parent`.id = old.id and `stg`.`parent`.delete_flg = 0
) as a
) = 0 THEN
DELETE FROM `prod`.`child` WHERE `prod`.`child`.id = old.id;
END IF;
END