How to add values in one table automatically when a condition is true - sql

Question

So, Here is the condition.
I have a User_tbl whose code is as follow
CREATE TABLE Users_tbl (
id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT,
user_type INT
);
user_type is either 0,1 or 2 .. If it is 0 then it is player , 1 is for coach and 2 is for audience.
Now, I want to create a new table which has lists of coach inside it . Whose schema will be
CREATE TABLE coach_tbl(
coach_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT
)
and what I need is that, when the entry which is placed in Users_tbl has user_type =1 then it should Trigger one other query which will create an entry in coach_tbl and fill the columns. It should happen dynamically .

Answer 1

The following TRIGGER would accomplish what you want :-
CREATE TRIGGER setup_coach
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coach_tbl (username, password) VALUES(new.username,new.password);
END
;
The following was used for testing the above :-
DROP TABLE IF EXISTS Users_tbl;
CREATE TABLE IF NOT EXISTS Users_tbl (
id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT,
user_type INT
);
DROP TABLE IF EXISTS coach_tbl;
CREATE TABLE IF NOT EXISTS coach_tbl(
coach_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT
);
CREATE TRIGGER setup_coach
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coach_tbl (username, password) VALUES(new.username,new.password);
END
;
INSERT INTO Users_tbl (username, password,user_type)
VALUES
('Fred','fred1234',0),
('Bert','bert1234',1),
('Harold','harold1234',0),
('Alan','alan1234',1);
The result being :-
Supplementary (aka Why not the above)
Storing the exact same values. i.e. duplicating them, is contrary to normalisation and could lead to issues. e.g. if (using the above) "Bert"'s name or "password" changed you'd have to change it in two places. As it stands there is no need to duplicate this data as it would be easily available
For example, if you wanted to list the coaches you could use :-
SELECT username FROM coach_tbl;
Using the following, though, returns exactly the same but without the additional table :-
SELECT username FROM Users_tbl WHERE user_type = 1;
Supposing you had coach specific information say for example the number of times coaching then you could have an additional table such as :-
CREATE TABLE IF NOT EXISTS coaching_information
(
user_id_reference INTEGER REFERENCES Users_tbl(id),
number_of_times_coaching INTEGER DEFAULT 0
)
;
Along with a TRIGGER to automatically add default coaching information :-
CREATE TRIGGER autoadd_coaching_information_entry
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coaching_information
(user_id_reference)
VALUES (new.id)
;
END
;
Note! no need to set the number_of_times_coaching column as it will default to 0.
Assuming that all TABLES have been emptied then using (again):-
INSERT INTO Users_tbl (username, password,user_type)
VALUES
('Fred','fred1234',0),
('Bert','bert1234',1),
('Harold','harold1234',0),
('Alan','alan1234',1);
results in :-
2 refers to Bert, 4 to Alan
You could then list all coaches who have not coached (chosen for laziness of not having to update coaching inforamtion) :-
SELECT 'Coach '||username||' is up for a coaching experience.' AS coaching_needed
FROM coaching_information
JOIN Users_tbl ON Users_tbl.id = coaching_information.user_id_reference
WHERE coaching_information.number_of_times_coaching < 1
The result would be :-
Say Bert changed name to Charles e.g. using UPDATE Users_tbl SET username = 'Charles' WHERE username = 'Bert';
Then just with the 1 change the results from the above query would be :-
The full SQL used for testing the above was :-
DROP TABLE IF EXISTS coach_tbl;
DROP TABLE IF EXISTS Users_tbl;
CREATE TABLE IF NOT EXISTS Users_tbl (
id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
username TEXT,
password TEXT,
user_type INT
);
DROP TRIGGER IF EXISTS setup_coach; -- get rid of defunct TRIGGER
CREATE TABLE IF NOT EXISTS coaching_information
(
user_id_reference INTEGER REFERENCES Users_tbl(id) ON DELETE CASCADE,
-- Note ON DELETE CASCADE will automatically delete a coach should
-- the coach's User_tbl entry be deleted i.e. the deletion is propoagted
-- to the children of the parent.
-- (could also use ON UPDATE CASCADE but unlikely to change the underlying id)
number_of_times_coaching INTEGER DEFAULT 0
)
;
DROP TRIGGER IF EXISTS autoadd_coaching_information_entry;
CREATE TRIGGER autoadd_coaching_information_entry
AFTER INSERT ON Users_tbl
WHEN new.user_type = 1
BEGIN
INSERT INTO coaching_information
(user_id_reference)
VALUES (new.id)
;
END
;
INSERT INTO Users_tbl (username, password,user_type)
VALUES
('Fred','fred1234',0),
('Bert','bert1234',1),
('Harold','harold1234',0),
('Alan','alan1234',1)
;
--
-- Note! oncommmenting this will change Bert's name to Charles
--UPDATE Users_tbl SET username = 'Charles' WHERE username = 'Bert';
--
SELECT 'Coach '||username||' is up for a coaching experience.' AS coaching_needed
FROM coaching_information
JOIN Users_tbl ON Users_tbl.id = coaching_information.user_id_reference
WHERE coaching_information.number_of_times_coaching < 1