How to structure an SQL table with metadata - sql

Question

So I am an SQL noobie, and I would like to organize a structured database that has metadata and data in SQLite. I am not sure how to do this, and I have looked around at different internet sites but I haven't found anything helpful.
Basically what I would want is something like this (using different data collection stations as an example):
SQL TABLE:
Location
Lat
Long
Other Important info about the station
And then somehow when I query this table and want to see info about specific stations data I would be able to pull up the data that would look something like this:
datetime data
1/1/1980 11.6985
1/2/1980 43.6431
1/3/1980 54.9089
1/4/1980 63.1225
1/5/1980 72.4399
1/6/1980 79.1363
1/7/1980 82.2778
1/8/1980 86.0785
1/9/1980 86.8612
1/10/1980 84.3342
1/11/1980 80.4646
1/12/1980 77.1508
1/13/1980 74.827
1/14/1980 73.387
1/15/1980 72.1774
1/16/1980 71.6423
Since I don't know much about table hierarchy, I don't know how to do this, but I feel like it is probably possible. Any help would be appreciated!

Answer 1

using different data collection stations
Immediately indicates that a separate table for stations should be used and that the readings should relate to/associate with/reference the stations table.
For the stations table you could have something like :-
CREATE TABLE IF NOT EXISTS stations (id INTEGER PRIMARY KEY, station_name TEXT, station_latitude REAL, station_longitude REAL);
This will create a table (if it doesn't already exist) that has 4 columns :-
The first column id is a unique identifier that will be generated automatically and is what you would use to reference a specific station.
The second column, station_name is for the name of the station an is of type TEXT.
The third and fourth columns are for the stations location according to lat and long.
You could add a couple of stations using :-
INSERT INTO stations (station_name, station_latitude,station_longitude) VALUES("Zebra", 100.7892, 60.789);
INSERT INTO stations (station_name, station_latitude,station_longitude) VALUES("Yankee", 200.2967, 95.234);
You could display/return these using :-
SELECT * FROM stations
that is SELECT all columns (*) FROM the table called stations, the result would be :-
Next you could create the readings table e.g. :-
CREATE TABLE IF NOT EXISTS readings(recorded_datetime INTEGER DEFAULT (datetime('now')), data_recorded REAL, station_reference INTEGER);
This will create a table named readings (if it doesn't already exist) it will have 3 columns :-
recorded_datetime which is of type INTEGER (can store integer of up to 8 bytes i.e. pretty large). This will be used to store a time stamp. Although perhaps not what you want, but as an example, a default value will be used, the current datetime, if no value is specified for this column.
data_recorded as a REAL that is for the data.
station_reference this will refer to the station's id.
You could then insert a reading for the for the Zebra station using :-
INSERT INTO readings (data_recorded,station_reference) VALUES(11.6985,1);
As the record_datetime column has not been provided then the current datetime will be used.
If :-
INSERT INTO readings VALUES(datetime('1980-01-01 10:40'),11.6985,1);
Then this reading would be for 1/1/1980 at 10:40 for station 1.
Using :-
INSERT INTO readings VALUES(datetime('1980-01-01 10:40'),13.6985,2);
INSERT INTO readings VALUES(datetime('1966-03-01 10:40'),15.6985,2);
INSERT INTO readings VALUES(datetime('2000-01-01 10:40'),11.6985,2);
Will add some readings for Yankee station (id 2).
using SELECT station_reference, recorded_datetime, data_recorded FROM READINGS; will select all the columns but the station_reference will be the first column in the result etc e.g. :-
The obvious progression is to display the data including the respective station. For this a JOIN will be used. That is the readings table will be joined with the stations table where the respective stations details are according to the station_refrence value matching the station's id.
However, let's say that we wanted the Station info to be something like stationname (Long=???? - Lat=????) date/time data and be sorted according to station name and then according to date/time. Then the following could be used :-
SELECT
stations.station_name ||
'(Long='||station_longitude||' - Lat='||station_latitude||')'
AS stationinfo,
readings.recorded_datetime,
readings.data_recorded
FROM readings
JOIN stations ON readings.station_reference = stations.id
ORDER BY stations.station_name ASC, readings.recorded_datetime
Note this is shown more of an example that you can do quite complex things in SQL, rather than there being an expectation of fully understanding the coding.
This would result in :-
You may (or some would) argue but why can't I just have a single table with reading, datetime, station name, station latitude, station longitude.
Well you could. BUT :-
Say there were a directive to change station Zebra's name then you'd have to trawl through all the rows to and change the name numerous times. Easy to code but relatively costly in terms of resource usage. Using the two tables means that just a single update is required.
For each row you would have to duplicate data very likely wasting disk space and thus increasing the resources needed to access the data. That is Zebra would take at least 5 bytes, Real's take 8 bytes (2 of them) so that's 21 bytes. A reference to one occurrence of that repeated data would take a maximum of 8 bytes for an integer (initially just a single byte). So there would be a cost of 13 bytes per reading.