SQL solve select basic statement

The phenomenon and background of the problem

The title is as follows
From the order_items table, get the items
for order #6
where the total price is greater than 30

Problem related code , Do not paste screenshots

My code is as follows
SELECT *, quantity * unit_price AS total_price
FROM order_items
WHERE order_id=6 AND total_price > 30

Operation results and error reporting contents

Error Code: 1054. Unknown column 'total_price' in 'where clause'

My solution ideas and tried methods

The correct solution is as follows
SELECT *
FROM order_items
WHERE order_id = 6 AND total_price>30

What I want to achieve

because column There is no total price column , So I want the output to show quantity * unit_price The numerical , But it's always wrong ……

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Take the answer ：

Alias cannot be used in query criteria , Revised as follows :

SELECT *, quantity * unit_price AS total_priceFROM order_itemsWHERE order_id=6 AND quantity * unit_price > 30

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