how to connect users with mysql in mobile apps? Login permissions
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This is the first time I make a database for user interaction and I have some "silly" questions but I do not know how to google them to have a correct answer so here it is:

**What I want:**

I want to have a database where there will be users that have writen comments and articles. I will have user critical information such as name and addres and maybe credit card that I will have to recover it.

**What I have done**

I have create a database with a table for users with its information and then related to a table with comments and an other with articles.

**My problems**

1) When you do a db connection, do you do every time with the same user (of course not root) and then you compare the nickname and pass? That's what I have but it's pretty strange for me because if anyone knows my user and pass to connect to db will have all the information. I have thougth of having an account for each user but then how I can restrict to add//erase/see only things for their accounts?

2) I have read  some questions and now I know I have to store passwords and compare them with bcrypt. Also I know credit card is not recomendable to store so probabilly I won't do it but for the rest of things (address, name) which is the best way to store them?

3) If an user does a connection and it's probabilly that will do more in a short time, is it better to close and open the connection each time? how can I control the session? Code is writen in php for connecting mobile devices to mysql.