PHP/MySQL Compare against a date - php

Question

I'm running into a little issue concerning a datetime picker and MySQL.
I have a PHP script that should get records before (and including) the selected day. However, the dataset returns empty.
Here's the SQL part of the script:
$sql = 'SELECT `pro_title`,
`pro_part_number`,
`name` AS flag_name,
`old_val`,
`new_val`
FROM `products`
INNER JOIN `flags` ON `id` = `pro_flag_id`
INNER JOIN `flag_history` ON `pro_part_number` = `part`
WHERE `pro_flag_id` IN(:flags)
AND STR_TO_DATE(`ts`, "%y-%m-%d") <= :dateTs;';
I then use PDO to bind the params:
array(
':flags' => implode(',', $flags), # this outputs 1,2,3
':dateTs' => $date # this outputs 2019-04-30
)
I've also tried changing <= to >= to no avail (not that it should work, but thought I'd try).
I've come across a good few SO posts but nothing has actually got me there. Here is the description of the flag_history table (where ts is stored)
MariaDB [mastern]> describe `flag_history`;
+---------+-------------+------+-----+-------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+-------------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| part | varchar(25) | NO | | NULL | |
| ts | datetime | YES | | CURRENT_TIMESTAMP | |
| old_val | int(4) | YES | | NULL | |
| new_val | int(4) | YES | | NULL | |
+---------+-------------+------+-----+-------------------+----------------+
And some example data:
MariaDB [mastern]> select * from `flag_history` order by `id` desc limit 5;
+-------+----------+---------------------+---------+---------+
| id | part | ts | old_val | new_val |
+-------+----------+---------------------+---------+---------+
| 24026 | PART-001 | 2019-04-30 09:42:22 | 0 | 3 |
| 24025 | PART-002 | 2019-04-30 09:42:22 | 0 | 3 |
| 24024 | PART-003 | 2019-04-30 09:42:22 | 0 | 3 |
| 24023 | PART-004 | 2019-04-30 09:42:22 | 0 | 3 |
| 24022 | PART-005 | 2019-04-30 09:42:22 | 0 | 3 |
+-------+----------+---------------------+---------+---------+
Then, using PART-001 to make sure the flag_id is actually set:
MariaDB [mastern]> select `pro_flag_id` from `products` where `pro_part_number` = "PART-001";
+-------------+
| pro_flag_id |
+-------------+
| 3 |
+-------------+
So I'm not really sure what's going wrong, the logic and everything to me (MySQL newb) looks like it should work but it's giving me empty data. I also tried changing the INNER JOIN's to LEFT JOIN's but again, didn't work.
What am I doing wrong?

Answer 1

I managed to solve it. As I'm really reading the flag_history table, I changed the main SELECT focus to flag_history, revised SQL:
$sql = 'SELECT `old_val`, `new_val`, `ts`, `flags`.`name` AS flag_name, `pro_part_number`, `pro_title`
FROM `flag_history`
INNER JOIN `products` ON `pro_part_number` = `part`
INNER JOIN `flags` ON `pro_flag_id` = `flags`.`id`
WHERE `ts` <= :dateTs;';
I slowly added in the INNER JOIN's and managed to get it working when using flag_history. I think the issue actually may have been down to the id field. Being an ambiguous field (flags and flag_history have the id column). Weirdly, I wasn't getting that error though (maybe as I wasn't selecting). Either way managed to resolve it by being more specific with my select and going from the read-table rather than joining it.
On a further note, removing the flags segment from the JOIN shows the constraint error. So my guess is that it didn't show first time as I was reading from a different table.