Difficulties in Database Development

I am a newbie in development and have encountered several problems in database development.
1: I made a connection to the database. From is running for half a day.
2: I added a button to connect to the database on the interface. When I click Connect to the database, the SQL chart is displayed.
3: The loading process is particularly slow when connecting to the database.
4: there will be 2-5 million data in the data table. If all the data is loaded into the memory, it will definitely affect the system speed. How can this problem be solved.


I want to ask my predecessors how to solve the problems you encounter when you are working on a project.
For example, how can I solve this problem when a new control encounters something that doesn't happen on its own.

Thank you for disturbing your predecessors.

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