[Tax] add FK to tax/sales_order_tax again

[Hanmac]

Description (*)

This Fixes the Missing FK between sales_order_tax and sales_flat_order

Right now, when an order gets deleted, the cascade deletes the sales_flat_order_item
and then the cascade deletes sales_order_tax_item,
but sales_order_tax stays with now the order_id pointing to an order that doesn't exist anymore.

That could cause in the wrong taxes to be displayed.

The FK existed before as FK_SALES_ORDER_TAX_ORDER, but got removed ages ago.

The only other tables that misses the FK are these ones, but they are referenced via creditmemo/invoice/shipment:

• sales_flat_creditmemo_grid
• sales_flat_invoice_grid
• sales_flat_shipment_grid
• sales_flat_shipment_track

Manual testing scenarios (*)

1. ...
2. ...

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[Hanmac]

@sreichel should be easy to merge? Or is it controversial?

[kiatng]

Any idea why was the FK dropped? For stores with large tables, I often experienced MySQL timeout or errors when adding index or modifying tables. Is this update safe? Will it break production?

[Hanmac]

Any idea why was the FK dropped? For stores with large tables, I often experienced MySQL timeout or errors when adding index or modifying tables. Is this update safe? Will it break production?

The FK there should be minimal, sales_order_tax isn't called that often without Order anyway.

[sreichel]

@sreichel should be easy to merge? Or is it controversial?

lgtm. Just dont know why it has been changed.

[Hanmac]

It's 13–14 years ago, probably no one remembers that

[sreichel]

Some times you find something in release notes or stackexchange ... but no.

[kiatng]

I am still not sure:

1. For large table, timeout may occur, I have a million entries in production
2. Missing orders in the sales table, meaning orphaned records in the tax table, MySQL may complain.

For ref, cursor AI suggest this:

// First, clean up orphaned records
$this->getConnection()->query("
    DELETE t FROM {$taxTable} t 
    LEFT JOIN {$orderTable} o ON t.order_id = o.entity_id 
    WHERE o.entity_id IS NULL
");

[Hanmac]

@kiatng yeah I should probably delete orphaned tax entries