将datetime列作为表中的外键是否安全？

I have two tables. Table A and B. Table A has a column with auto increment as primary key.

id    name       date_created
1     Kletian    12-12-12 12:12:12  
2     Vormav     12-12-12 12:12:13
3     Agrias     12-12-12 12:12:14
4     Ramza      12-12-12 12:12:15

Table B should has a foreign key referencing the id in table A. But since the id is auto increment (generated by mysql) I can't assign it using server side programming (I use PHP to insert). But, In table A, there is a column date_created with datetime attribute.

Normally, this is the table B should looks like:

id     images
1      abc.jpg
1      def.png
1      ghi.jpg
2      jkl.png
3      mno.jpeg
3      pqr.png

and this is my plan for table B:

date_created           images
12-12-12 12:12:12      abc.jpg
12-12-12 12:12:12      def.png
12-12-12 12:12:12 
12-12-12 12:12:13
12-12-12 12:12:14       
12-12-12 12:12:14      pqr.png

Note:

• Getting the auto increment value via server side programming (PHP) is not reliable. Since user can delete a record and messed up the order.
• I have limited privilege to change the table structure. Minor changes is okay, but major changes is prohibited.
• Is my plan safe or there are another alternatives?

Sequence number: Take one column in table A which you increment when new entry is inserted ( not auto-increment ) e.g:

seq_no | name 
  1    |  Kletian
  3    |  Agrias

So when you want to do new entry in a table A, just get the MAX() of seq_no and increment it by 1.

Also in table B, make seq_no as like a foreign key, as:

seq_no | images
  1    |  abc.jpg
  3    |  efg.jpg

Here is what you would want for your table DDL (schema):

CREATE TABLE IF NOT EXISTS `table_a` (
  `id`                  MEDIUMINT   NOT NULL AUTO_INCREMENT,
  `name`                TEXT        NOT NULL,
  `created_date`        TIMESTAMP   NOT NULL DEFAULT NOW(),
  PRIMARY KEY (`id`)
);

CREATE TABLE IF NOT EXISTS `table_b` (
  `id`                  MEDIUMINT   NOT NULL AUTO_INCREMENT,
  `image`               TINYTEXT    NOT NULL,
  `created_date`        TIMESTAMP   NOT NULL DEFAULT NOW(),
  `table_a_id`          MEDIUMINT   NOT NULL,
  PRIMARY KEY (`id`),
  FOREIGN KEY (`table_a_id`) REFERENCES table_a(id) ON DELETE CASCADE
);

Table B will have a foreign key reference to Table A.

I am not sure if are able to make those changes, but that would be the ideal solution.