SQLite: trigger to check newly inserted row against limits in another table - sqlite

Question

I have a database with the following schema:
Sensors (
ID INTEGER PRIMARY KEY AUTOINCREMENT
UNIQUE
NOT NULL,
SITE_ID INTEGER REFERENCES Sites (ID)
NOT NULL,
NAME TEXT UNIQUE
NOT NULL
);
Sites (
ID INTEGER PRIMARY KEY AUTOINCREMENT
UNIQUE
NOT NULL,
NAME TEXT UNIQUE
NOT NULL
);
Data (
SENSOR_ID INTEGER REFERENCES Sensors (ID)
NOT NULL,
COUNT INTEGER NOT NULL,
TIME DATETIME NOT NULL,
TYPE TEXT NOT NULL,
VALUE REAL NOT NULL,
PRIMARY KEY (
SENSOR_ID,
COUNT,
TIME,
TYPE
)
);
Limits (
SITE_ID INTEGER REFERENCES Sites (ID)
NOT NULL,
TYPE TEXT NOT NULL,
HIGH REAL NOT NULL,
LOW REAL NOT NULL,
PRIMARY KEY (
SITE_ID,
TYPE
)
);
Data contains all the data for all sensors and sites, Data has a few different types. The limits have a row for each type of data for each of the sites. I want to create a table identical to Data (called Warnings) containing only the rows where the value lies outside of the limits in Limit.
I want to do this with a trigger because the limits can change and the rows are added to data sporadically.
Here's my best attempt so far:
CREATE TRIGGER VALUE_OUT_OF_RANGE
AFTER INSERT
ON Data
WHEN NEW.VALUE < (SELECT Limits.LOW FROM Limits INNER JOIN Sensors ON (Sensors.SITE_ID = Limits.SITE_ID) WHERE (Sensors.ID = NEW.SENSOR_ID AND Limits.TYPE = NEW.TYPE))
BEGIN
INSERT INTO Warnings(SENSOR_ID, COUNT, TIME, TYPE, VALUE) VALUES(NEW.SENSOR_ID, NEW.COUNT, NEW.TIME, NEW.TYPE, NEW.VALUE);
END;
In my attempt I've only checked against the lower limit, in the final trigger I would like to check that the value is between the LOW and HIGH limits.
I've tried the Select statement seperately and I get the data that I am looking for.
Any help or suggestion is greatly appreciated.

Answer 1

I managed to find a solution that works.
Posting it in case it helps anyone.
CREATE TRIGGER VALUE_OUT_OF_RANGE
AFTER INSERT
ON Data
FOR EACH ROW
WHEN NEW.VALUE < (
SELECT Limits.LOW
FROM Limits
JOIN
Sensors ON (Sensors.SITE_ID = Limits.SITE_ID)
WHERE (Sensors.ID = NEW.Sensor_ID AND
Limits.TYPE = NEW.TYPE)
LIMIT 1
)
OR
NEW.VALUE > (
SELECT Limits.HIGH
FROM Limits
JOIN
Sensors ON (Sensors.SITE_ID = Limits.SITE_ID)
WHERE (Sensors.ID = NEW.Sensor_ID AND
Limits.TYPE = NEW.TYPE)
LIMIT 1
)
BEGIN
INSERT INTO Warnings (
SENSOR_ID,
COUNT,
TIME,
TYPE,
VALUE
)
VALUES (
NEW.SENSOR_ID,
NEW.COUNT,
NEW.TIME,
NEW.TYPE,
NEW.VALUE
);
END;