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I am new to SQL, please advise.
I wish to logging incoming data from sensor every 5 seconds for future graph plotting
What is the best way to design database in MySQL?
Or Could I log and make average every minute, hour, day to reduce database size
Is it possible to use trigger function to make average when collect data over 1 minute ?
The answer is that it depends on how much data you are actually going to be logging, how often you are going to be querying it, and how fast your response time needs to be. If it’s just one sensor, every 5 seconds, you could probably go on for eternity without running into too many problems with regular sql queries to pull out averages, sums, etc. in a reasonable period of time.
I will say that from experience, you can do a lot with SQL and time series data, but you have to be very careful how you design your queries. I’ve worked with time series tables with billions of rows and tens of thousands of individual sensors among those rows; it’s possible to achieve very fast execution over that many time series rows, but you might spend a week trying to fine-tune the database. It’s definitely a trade-off between flexibility and speed.
Again, for your purposes, it probably is not going to make very much difference if you are just talking about one sensor; just write a regular SQL query. However, if you anticipate adding several hundred more sensors or increasing the sample rate, you may want to consider doing periodic “rollup” functions as you suggest. And in that case, I would be more inclined to write a custom solution using a NoSQL database (e.g. Cassandra, Couchbase, etc.) and using a program that runs periodically to do the rollup. If you are interested, I can provide details, but I really don’t think you will need to go that far.
This post has a pretty good discussion on storing time series data in SQL vs NOSQL: https://dba.stackexchange.com/questions/7634/timeseries-sql-or-nosql