The Shanghai Stock Exchange must choose Ping Jin to open positions on the same day. If it chooses to close the position, it will prompt the customer that the position is insufficient, which will lead to the rejection of the entrustment.
The Shanghai Stock Exchange clearly divides liquidation into liquidation (liquidation of historical position) and liquidation of current position (liquidation of current position), but Dalian Stock Exchange and Zhengzhou Stock Exchange have no division.
By default, the oldest position is liquidated. If your current position has two lots, 1 hand is a historical position (not today's opening), and 1 hand is today's opening, then by default, closing the historical position first will generate a handling fee, and closing the historical position will not generate a handling fee. From this perspective, the practice of the Shanghai Stock Exchange actually saves investors a handling fee.
Answer supplementary questions:
Personally, as an ordinary investor, there is not much difference in trading system, personal preferences and habits.
At present, there are Kingstar, Wenhua and Pengbo. Both have introduced fast trading systems with many functions, such as placing arbitrage orders and winning or losing orders, but they are a bit complicated for ordinary investors. Personally, I recommend Pengbo's new lightning hand, which has a friendly interface, just like the market and trading interface. After clicking on the market, the transaction bar below will automatically fill in the contents of the order, and the number of lots can be set by yourself. Moreover, the trading price of the trading bar is linked to the market, which is more convenient for short-term investors and can basically realize one-click trading. One-click cultural communication is similar to Pengbo's new Lightning Hand, but it has more comprehensive functions, such as drawing lines to trigger.