复杂些的MySQL的Update更新语句

以下是关联更新表字段，慎用

UPDATE  test_info ti
JOIN (
	SELECT
		al.unit_price_tax,
		al.amount,
		al.unit_price_tax * apll.amount AS line_amount,
		al.line_id
	FROM
		ac_line al
	JOIN test_info ti ON ti.line_id = al.ledger_id
) AS ap ON ap.line_id = ti.line_id
SET ti.line_amount = ap.line_amount