SQL Statement to get all entries in timerange based on identifier - database

Question

I'm storing interface data from my Router gathered through SNMP in a MariaDB. The data is structured in the following way (simplified):
id TIMESTAMP READING VALUE
============================================================
100 2020-04-15 11:29:51 if03_name eth0
101 2020-04-15 11:29:51 if03_totalBytesRx 654321
102 2020-04-15 11:29:51 if03_totalBytesTx 123456
103 2020-04-15 11:30:51 if03_totalBytesRx 765432
104 2020-04-15 11:30:51 if03_totalBytesTx 234567
Now to get the data received and transmitted for eth0 it is easily possible to select on the READING if03_totalBytesRx or if03_totalBytesTx.
For instance, I can execute the following query to get the average bits per second received at any given time:
SELECT
TIMESTAMP,
GREATEST(0,(VALUE - LAG(VALUE,1) OVER (ORDER BY TIMESTAMP))*8/(UNIX_TIMESTAMP(TIMESTAMP) - UNIX_TIMESTAMP(LAG(TIMESTAMP,1) OVER (ORDER BY TIMESTAMP)))) as value
FROM history
WHERE
READING = "if03_totalBytesRx"
Unfortunately, sometimes (I believe when an interface goes down and up again) the mapping between READING and interface changes, such that if03 is not eth0 any more (if03 could for instance be eth1 or also noSuchInstance), whereas eth0 is assigned another READING, for example if29:
id TIMESTAMP READING VALUE
============================================================
200 2020-04-15 12:16:51 if03_totalBytesRx 876543
201 2020-04-15 12:16:51 if03_totalBytesTx 345678
202 2020-04-15 12:17:51 if03_name noSuchInstance
203 2020-04-15 12:17:51 if03_totalBytesRx noSuchInstance
204 2020-04-15 12:17:51 if03_totalBytesTx noSuchInstance
205 2020-04-15 12:17:51 if29_name eth0
206 2020-04-15 12:17:51 if29_totalBytesRx 987654
207 2020-04-15 12:17:51 if29_totalBytesTx 456789
Note that if03_name is only stored in the DB when changed, not every minute.
Obviously that causes either no data when querying the READING if03_totalBytesRx (in the case of noSuchInstance) or false data, i.e. data from another interface.
What would be a viable way to select all the ifXX_totalBytesRx and ifXX_totalBytesTx for all the timeranges where the corresponding ifXX_name equals to eth0? (E.g. in the example above the union of 11:29:51 to 12:17:50 using if03 plus everything from 12:17:51 to NOW() using if29, assuming that id 207 is the last entry in the database)

Answer 1

Ok, I think I found a solution myself, however it is kind of slow, so I'm happy about any improvements:
First, I created a view ubnt that splits the original READING into a new field INTERFACE (the part before the underscore) and another field READING (the part after the underscore, reusing the name):
SELECT
id,
TIMESTAMP,
substring_index(READING,'_',1) AS INTERFACE,
substring_index(READING,'_',-1) AS READING,
VALUE
FROM history
WHERE READING like 'if%'
The second step is to create another view from this called ubnt_if that shows the timerange of a logical to physical interface mapping:
SELECT
TIMESTAMP AS START,
COALESCE(LEAD(TIMESTAMP,1) OVER ( PARTITION BY INTERFACE ORDER BY TIMESTAMP),NOW()) AS END,
INTERFACE AS LOGICAL,
VALUE AS PHYSICAL
FROM ubnt
WHERE READING = 'name'
The third step is to join the interface to the original data, based on the timestamp. For this, I used another view called ubnt_int:
SELECT
a.TIMESTAMP AS TIMESTAMP,
a.READING AS READING,
a.VALUE AS VALUE,
b.PHYSICAL AS INTERFACE
FROM (
ubnt a
LEFT JOIN ubnt_if b ON(
a.INTERFACE = b.LOGICAL AND
a.TIMESTAMP BETWEEN b.START AND b.END
)
)
This generates a table of data that I can filter based on the physical interface, not the "logical" interface that could change.
I was inspired by this answer to another question.