Creating trigger to compare dates from two tables [duplicate] - sqlite

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Checking if date in table B is between date in Table A before inserting SQLite
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I have two tables that both have separate start/end date values in them. One Project can contain many Plans, and a specific Plan start/end date should be between its Project start/end date. I dont know how to validate this, and I have tried to use triggers but I just cant figure it out. Can someone give me some pointers on what I'm doing wrong?
This is my trigger:
%%sql
CREATE TRIGGER beforeInsertInPlan BEFORE INSERT ON Plan FOR EACH ROW
BEGIN
SELECT proID.projectID FROM Project
INNER JOIN Project ON pID = Project.projectID
WHERE
And here are my two tables:
%%sql
DROP TABLE IF EXISTS Project;
CREATE TABLE Project (
projectID varchar(255) NOT NULL UNIQUE,
name varchar(255) NOT NULL DEFAULT ' ',
leader varchar(255) NOT NULL DEFAULT ' ',
budget varchar(255) NOT NULL DEFAULT '0',
startDate DATE NOT NULL DEFAULT '2000-12-31',
endDate DATE NOT NULL DEFAULT '2000-12-31'
CHECK (JulianDay(startDate) <= JulianDay(endDate)),
PRIMARY KEY (projectID)
);
and:
%%sql
DROP TABLE IF EXISTS Plan;
CREATE TABLE Plan (
pID varchar(255) NOT NULL UNIQUE,
projectID varchar(255) DEFAULT NULL,
name varchar(255) NOT NULL DEFAULT ' ',
startDate DATE NOT NULL DEFAULT ' ',
endDate DARE NOT NULL DEFAULT ' '
CHECK (JulianDay(startDate) <= JulianDay(endDate) AND (startDate >= Project.startDate) AND
(endDate <= Project.endDate)),
PRIMARY KEY (pID, projectID),
FOREIGN KEY (projectID) REFERENCES Project(projectID)
);

Answer 1

First a BEFORE INSERT trigger will probably result in nothing but issues. see https://sqlite.org/lang_createtrigger.html#cautions_on_the_use_of_before_triggers
So here's a trigger that I believe will work as intended albeit it deleting the inserted row:-
CREATE TRIGGER IF NOT EXISTS afterInsertInPlan
AFTER INSERT ON plan
WHEN (
(NOT (new.startdate) BETWEEN
(SELECT startdate FROM project WHERE projectID = new.projectID)
AND
(SELECT enddate FROM project WHERE projectID = new.projectID)
)
OR
(NOT (new.enddate) BETWEEN
(SELECT startdate FROM project WHERE projectID = new.projectID)
AND
(SELECT enddate FROM project WHERE projectID = new.projectID)
)
)
BEGIN
DELETE FROM plan WHERE pID = new.pID ;
END
;
Testing/Demo
The above was tested using :-
DROP TABLE IF EXISTS Project;
CREATE TABLE Project (
projectID varchar(255) NOT NULL UNIQUE,
name varchar(255) NOT NULL DEFAULT ' ',
leader varchar(255) NOT NULL DEFAULT ' ',
budget varchar(255) NOT NULL DEFAULT '0',
startDate DATE NOT NULL DEFAULT '2000-12-31',
endDate DATE NOT NULL DEFAULT '2000-12-31'
CHECK (JulianDay(startDate) <= JulianDay(endDate)),
PRIMARY KEY (projectID)
);
DROP TABLE IF EXISTS Plan;
CREATE TABLE Plan (
pID varchar(255) NOT NULL UNIQUE,
projectID varchar(255) DEFAULT NULL,
name varchar(255) NOT NULL DEFAULT ' ',
startDate DATE NOT NULL DEFAULT ' ' ,
endDate DATE NOT NULL DEFAULT ' ',
CHECK (endDate >= startDate),
PRIMARY KEY (pID, projectID),
FOREIGN KEY (projectID) REFERENCES Project(projectID)
);
DROP TABLE IF EXISTS trigger_log;
CREATE TABLE IF NOT EXISTS trigger_log (id INTEGER PRIMARY KEY, timestamp TEXT DEFAULT CURRENT_TIMESTAMP, trigger_text TEXT);
DROP TRIGGER IF EXISTS beforeInsertInPlan;
CREATE TRIGGER IF NOT EXISTS afterInsertInPlan
AFTER INSERT ON plan
WHEN (
(NOT (new.startdate) BETWEEN
(SELECT startdate FROM project WHERE projectID = new.projectID)
AND
(SELECT enddate FROM project WHERE projectID = new.projectID)
)
OR
(NOT (new.enddate) BETWEEN
(SELECT startdate FROM project WHERE projectID = new.projectID)
AND
(SELECT enddate FROM project WHERE projectID = new.projectID)
)
)
BEGIN
DELETE FROM plan WHERE pID = new.pID ;
INSERT INTO trigger_log (trigger_text) VALUES('DELETED FROM Plan Table due to date(s) not within project. pID was '||new.pID);
END
;
INSERT INTO project VALUES ('P1','P1','Mary',100,'2021-09-01','2022-09-30');
INSERT INTO plan VALUES ('P1P1','P1','Plan1','2021-09-01','2022-09-30');
INSERT INTO plan VALUES ('P1P2','P1','Plan2','2021-08-01','2022-09-30'); /* X */
INSERT INTO plan VALUES ('P1P3','P1','Plan3','2021-09-01','2022-10-30'); /* X */
INSERT INTO plan VALUES ('P1P4','P1','Plan4','2020-09-01','2022-10-30'); /* X */
INSERT INTO plan VALUES ('P1P5','P1','Plan5','2021-09-01','2021-10-01');
INSERT INTO plan VALUES ('P1P6','P1','Plan6','2021-10-01','2021-11-01');
INSERT INTO plan VALUES ('P1P7','P1','Plan7','2021-11-01','2021-12-01');
SELECT * FROM plan;
/* Cleanup Environment */
SELECT * FROM trigger_log;
DROP TABLE IF EXISTS trigger_log;
DROP TRIGGER IF EXISTS beforeInsertInPlan;
DROP TABLE IF EXISTS Plan;
DROP TABLE IF EXISTS Project;
When run then the results are :-
The Plan's in the plan table:-
i.e. those commented with an X (3) were not inserted
The trigger_log (used to confirm triggering when testing) :-
i.e. the 3 commented with an X that were not inserted have been logged accordingly.
Example of why not to use a BEFORE INSERT trigger
Swapping the trigger to use BEFORE INSERT and :-
All are inserted :-
None are deleted even though logged:-
i.e. nothing to delete as nothing has been inserted.