MySQL programmer to management/maintain large databases

If you think you are the right candidate for us, please, answer the questions below:

“SELECT x, y FROM z WHERE x = ‘abc’ AND y = ‘’def” query in MySQL is being executed too long, the table has 50m rows. What’s the best way to analyze and resolve the issue? Please, explain briefly.

The export of 1m rows from MySQL throws a 504 error. The script is simple, it gets all records and converts them to CSV file. The operation takes more than 5 seconds. The web server returns a 504 error if the request executes more than 5 seconds. How would you build the “export data” feature without updating the web-server configuration so it won’t throw a 504 error message to the user? Please, explain briefly.

Looking forward to hearing from you.

Best regards,