At what price is a transaction carried out on the exchange?

Question

Fintech

For example, I will describe the situation:
Several
sell orders are received on the exchange

• 2 BTC at a price of at least 11,000 USD at 10:00
  
• 1.2 BTC at a price of at least 10,000 USD at 10:20
  

To purchase

• 1.5 BTC at a price of no more than 9000 USD at 10:10
  
• 2.2 BTC at a price of no more than 12000 USD at 10:30
  

Thus, an order received at 10:30 can be satisfied, and first it must be partially closed by an order at 10:00, and then the rest by an order at 10:20.
The question is, at what price to conduct a transaction, at the order price at 10:00 or the order price at 10:30?
UPD
To make it more clear, I will repeat the clarification from the comments:

Conditionally - if you execute the one at 10:00 at 11k, then the seller will be "offended", because his application could be executed at 12k. If you execute an order for 12k, then the "buyer" will be offended, because it is more profitable for him to buy for 11k. The bottom line is, which one should be given priority?

Answer 1

There are two approaches to writing an exchange
* the first - all transactions are limit, i.e. they are not executed immediately, even if there is a suitable counter order. On the exchange, a special bot is constantly spinning in the cycle, which buys and sells orders with its own money (it is quite possible to put a block on the cancellation of orders that it processes so that the processing of several is atomic, but this is not necessary)
as a result, intersecting orders at different prices exchange can execute at its own prices, according to what the clients indicated, and take the difference in their pocket - formally everything is OK, the clients asked for such a price and they received it
* the second - if the deal at the price crosses someone else's limit order - it becomes a filled order, i.e. 2 or more orders are executed, at the price indicated by clients in limit orders
. Thus, the client can safely indicate a price with a margin beyond the border of the current market edge, but the final price will be more profitable for him. Some exchanges even make a special type of orders without specifying a price, just for buying and selling on the current glass.
Most often, cryptocurrency exchanges choose the second method.
Both solutions provide a lot of options for fraud on the part of the exchange (this is especially true if you play with margin trading), I don’t know how it is with regulation, but this is not yet the case in cryptocurrencies.

Answer 2

By 10:00, of course. But in reality, first 1.2btc will be bought at 10 thousand, and then another 1btc will be bought at 11

Answer 3

and first it must be partially closed by an order at 10:00, and then the rest by an order at 10:20

who teaches you to count like that? )) to give a piece for a healthy life?
at 10:30 you give 1.2 out of 10_20 and 1 and 1 out of 10_00

Answer 4

The stock market doesn't work that way. There is no "no less" for sale.
When placing a sell order, a specific price is indicated. And the order will be executed only at this price. Nothing more, nothing less.