使用案例来确定应该加入哪个表

Question

我有四张表products，product_histories，vendor_invoices和invoices

这是我开发的查询

SELECT p.product_id, product_name, vendor_name FROM products AS p
INNER JOIN product_histories AS ph ON p.product_id = ph.product_id
CASE
    WHEN ph.history_type = "P" THEN
        LEFT JOIN vendor_invoices AS vi ON link_id = vi.vi_id

    WHEN ph.history_type = "S" THEN
        LEFT JOIN invoices AS i ON i.invoice_id = link_id
END
ORDER BY ph_id ASC

如果ph.history_type为P，我应该加入vendor_invoices，如果是S，那么它应该加入invoices。但它表示存在语法错误。 任何人都可以帮我解决这个问题吗？或者可以展示更好的方法来解决这个问题。