trigger insert different row - sqlite

The sqlite3 trigger that I want to create might or might not be possible with sql. Five tables are involved:
Members Groups GroupMembers Accounts
mId |name| accId gId | name | accId gId | mId accId | balance
Orders
oId | accId | ammount
When someone deletes a group, I want to make an order for each of the group members with the average of the group balance. So it should do something like this:
CREATE NEW TRIGGER triggername
BEFORE DELETE ON Groups
WHEN ((SELECT balance FROM Accounts WHERE accId=OLD.accId) = 0)
FOR EACH ROW IN
(SELECT accId
FROM GroupMembers JOIN Members ON GroupMembers.mId = Members.mId
WHERE GroupMembers.gId = OLD.gId)
BEGIN
INSERT INTO Orders(accId,ammount) VALUES(accId,
(SELECT balance FROM Accounts WHERE accId = OLD.accId)
/
(SELECT SUM(mId) FROM GroupMembers WHERE gId = OLD.gId)
);
END
The question is: is it possible to create a FOR EACH ROW in any other table than the table at which the trigger applies? Is it possible to put the WHEN statement before the FOR EACH statement?

As documented, there is no such a thing as a FOR EACH ROW IN ... clause.
However, the INSERT statement can use a SELECT statement as the source of the data to be inserted.
Write a SELECT statement that returns one row for each group member:
CREATE TRIGGER triggername
AFTER DELETE ON Groups
FOR EACH ROW
BEGIN
INSERT INTO Orders(accId, amount)
SELECT accId,
(SELECT balance
FROM Accounts
WHERE accId = OLD.accId) /
(SELECT COUNT(*)
FROM GroupMembers
WHERE gId = OLD.gId)
FROM Members
WHERE mId IN (SELECT mId
FROM GroupMembers
WHERE gId = OLD.gId);
END;
(I dropped the balance = 0 filter.)

Related

INSTEAD OF AND COMPOUND INTEGER

C. Create an INSTEAD OF row trigger on EMP_VU that increases the current count for a department by 1 if a new employee is added and subtracts 1 from the count for a department if an employee is deleted
create or replace trigger count_trigger
instead of insert or delete on emp_vu
begin
if deleting then
update dept_count
set count_emps = count_emps - 1
where dept_id = :OLD.department_id ;
elsif inserting then
update dept_count
set count_emps = count_emps + 1
where dept_id = :NEW.department_id ;
end if ;
end ;
/
D. Look at the counts for all departments in DEPT_COUNT. Test to see if your trigger fires correctly by inserting a row into EMP_VU. Look at the count for the department of the new employee. Delete a row from EMP_VU. Look at the count for the department where the employee was just deleted.
SELECT * FROM dept_count;
INSERT INTO emp_vu VALUES (606, 'Sillins', 90);
DELETE FROM emp_vu WHERE employee_id = 606;
Excuse me is there anyone help to repair this query?

Updating a singular row in a trigger SQLite

Table rental has values (ID, odo_out, date),
table vehicle has values (ID, odo, car),
both with more columns but not relevant to this.
I have attempted to create a trigger:
CREATE TRIGGER odo_update AFTER INSERT ON rental
BEGIN
UPDATE rental SET odo_out = (SELECT Vehicle.odo FROM Vehicle WHERE rental.ID = Vehicle.ID)
WHERE EXISTS (SELECT * FROM Vehicle WHERE Vehicle.ID = rental.ID);
END;
which should detect a NULL for rental.odo_out and replace it with the value in Vehicle.odo for corresponding ID. This does work, but it updates every row in table, whereas I want it to ONLY update the row with NULL, ie the new row being inserted. An ID can be repeated multiple times in the rental table. How can I do this?
You must set the condition so that only the new row is updated.
This is where you need the keyword NEW to refer to the columns of the new row:
CREATE TRIGGER odo_update AFTER INSERT ON rental
WHEN NEW.odo_out IS NULL
BEGIN
UPDATE rental
SET odo_out = (SELECT odo FROM Vehicle WHERE ID = NEW.ID)
WHERE ID = NEW.ID;
END;

SQLite Nested Query for maximum

I'm trying to use DB Browser for SQLite to construct a nested query to determine the SECOND highest priced item purchased by the top 10 spenders. The query I have to pick out the top 10 spenders is:
SELECT user_id, max(item_total), SUM (item_total + shipping_cost -
discounts_applied) AS total_spent
FROM orders AS o
WHERE payment_reject = "FALSE"
GROUP BY user_id
ORDER BY total_spent DESC
LIMIT 10
This gives the user_id, most expensive item they purchased (not counting shipping or discounts) as well as the total amount they spent on the site.
I was trying to use a nested query to generate a list of the second most expensive items they purchased, but keep getting errors. I've tried
SELECT user_id, MAX(item_total) AS second_highest
FROM orders
WHERE item_total < (SELECT user_id, SUM (item_total + shipping_cost -
discounts_applied) AS total_spent
FROM orders
WHERE payment_reject = "FALSE"
GROUP BY user_id
ORDER BY total_spent DESC
LIMIT 10)
group by user_id
I keep getting a row value misused error. Does anyone have pointers on this nested query or know of another way to find the second highest item purchased from within the group found in the first query?
Thanks!
(Note: The following assumes you're using Sqlite 3.25 or newer since it uses window functions).
This will return the second-largest item_total for each user_id without duplicates:
WITH ranked AS
(SELECT DISTINCT user_id, item_total
, dense_rank() OVER (PARTITION BY user_id ORDER BY item_total DESC) AS ranking
FROM orders)
SELECT user_id, item_total FROM ranked WHERE ranking = 2;
You can combine it with your original query with something like:
WITH ranked AS
(SELECT DISTINCT user_id, item_total
, dense_rank() OVER (PARTITION BY user_id ORDER BY item_total DESC) AS ranking
FROM orders),
totals AS
(SELECT user_id
, sum (item_total + shipping_cost - discounts_applied) AS total_spent
FROM orders
WHERE payment_reject = 0
GROUP BY user_id)
SELECT t.user_id, r.item_total, t.total_spent
FROM totals AS t
JOIN ranked AS r ON t.user_id = r.user_id
WHERE r.ranking = 2
ORDER BY t.total_spent DESC, t.user_id
LIMIT 10;
Okay, after fixing your table definition to better reflect the values being stored in it and the stated problem, and fixing the data and adding to it so you can actually get results, plus an optional but useful index like so:
CREATE TABLE orders (order_id INTEGER PRIMARY KEY
, user_id INTEGER
, item_total REAL
, shipping_cost NUMERIC
, discounts_applied NUMERIC
, payment_reject INTEGER);
INSERT INTO orders(user_id, item_total, shipping_cost, discounts_applied
, payment_reject) VALUES (9852,60.69,10,0,FALSE),
(2784,123.91,15,0,FALSE), (1619,119.75,15,0,FALSE), (9725,151.92,15,0,FALSE),
(8892,153.27,15,0,FALSE), (7105,156.86,25,0,FALSE), (4345,136.09,15,0,FALSE),
(7779,134.93,15,0,FALSE), (3874,157.27,15,0,FALSE), (5102,108.3,10,0,FALSE),
(3098,59.97,10,0,FALSE), (6584,124.92,15,0,FALSE), (5136,111.06,10,0,FALSE),
(1869,113.44,20,0,FALSE), (3830,129.63,15,0,FALSE), (9852,70.69,10,0,FALSE),
(2784,134.91,15,0,FALSE), (1619,129.75,15,0,FALSE), (9725,161.92,15,0,FALSE),
(8892,163.27,15,0,FALSE), (7105,166.86,25,0,FALSE), (4345,146.09,15,0,FALSE),
(7779,144.93,15,0,FALSE), (3874,167.27,15,0,FALSE), (5102,118.3,10,0,FALSE),
(3098,69.97,10,0,FALSE), (6584,134.92,15,0,FALSE), (5136,121.06,10,0,FALSE),
(1869,123.44,20,0,FALSE), (3830,139.63,15,0,FALSE);
CREATE INDEX orders_idx_1 ON orders(user_id, item_total DESC);
the above query will give:
user_id item_total total_spent
---------- ---------- -----------
7105 156.86 373.72
3874 157.27 354.54
8892 153.27 346.54
9725 151.92 343.84
4345 136.09 312.18
7779 134.93 309.86
3830 129.63 299.26
6584 124.92 289.84
2784 123.91 288.82
1619 119.75 279.5
(If you get a syntax error from the query now, it's because you're using an old version of sqlite that doesn't support window functions.)

confused on how to properly use %rowtype for many tables

I'm attempting to create a derived table of country data from several other tables. Those tables look something like this:
Countries
ID | Name
Country_demographics
ID | date | Population | urban_pop | birth_rate
country_financials
ID | date | GDP | GDP_per_capita
Now, I'm trying to make a new table with
New_Table
ID | Name | date | population | urban_pop | birth_rate | gdp | gdp_per_capita
I have a stored procedure that currently looks something like this:
CREATE OR REPLEACE PROCEDURE SP_COUNTRY (
chunkSize IN INT
) AS
--create tables to hold IDs and stats
TYPE idTable IS TABLE OF COUNTRIES.ID%TYPE;
TYPE dateTable IS TABLE OF COUNTRY_DEMOGRAPHICS.EVALUATION_DATE%TYPE;
TYPE totPopTable IS TABLE OF COUNTRY_DEMOGRAPHICS.POPULATION_TOTAL_COUNT%TYPE;
TYPE urbanPopTable IS TABLE OF COUNTRY_DEMOGRAPHICS.POPULATION_URBAN_COUNT%TYPE;
--constructors
ids idTable;
dates dateTable;
totpop totPopTable;
urbanpop urbanPopTable;
--cursors
CURSOR countryCur IS
SELECT c.ID,cd.EVALUATION_DATE,cd.POPULATION_TOTAL_COUNT,cd.POPULATION_URBAN_COUNT
FROM COUNTRIES c,COUNTRY_DEMOGRAPHICS cd
WHERE c.id=cd.COUNTRY_ID
ORDER BY ID,EVALUATION_DATE;
BEGIN
dbms_output.enable(999999);
--open cursor
OPEN countryCur;
LOOP
--fetch and bulk collect
FETCH countryCur BULK COLLECT INTO ids,dates,totpop,urbanpop
LIMIT chunkSize;
--loop over collections
FOR j in ids.FIRST..ids.LAST
LOOP
--populate record
country.COUNTRY_ID := ids(j);
country.EVALUATION_DATE := dates(j);
country.POPULATION_TOTAL_COUNT := totpop(j);
country.POPULATION_URBAN_COUNT := urbanpop(j);
--update/insert table with record (much confusion here on how to update/insert and check if already exists in derived table..)
UPDATE NEW_TABLE SET ROW = country WHERE COUNTRY_ID = ids(j);
dbms_output.put_line('id: ' || country.COUNTRY_ID || ' date: ' || country.EVALUATION_DATE);
dbms_output.put_line(' pop: ' || country.POPULATION_TOTAL_COUNT || ' urban: ' || country.POPULATION_URBAN_COUNT);
END LOOP;
END LOOP;
--close cursor
CLOSE countryCur;
END;
As you can see, I'm using a different table type for each piece of data. I then plan on making a loop and then just inserting/updating in my new_table. I think there must be a better way to do this with %rowtype, or maybe creating a record and inserting the record? I'm not sure
Unless I'm missing something by simplifying this, and assuming cd.date and cf.date are equal, this should work:
INSERT INTO NEW_TABLE (ID, Name, date, population, urban_pop, birth_rate, gdp, gdp_per_capita)
values
(select c.id, c.name, cd.date,
cd.population, cd.urban_pop, cd.birthrate,
cf.gdp, cf.gdp_per_capita)
from Countries c, country_demographics cd, country_financials cf
where c.id = cd.id
and cd.id = cf.id);
Edit: Use the MERGE statement to update or insert depending on if the primary key exists:
MERGE INTO NEW_TABLE nt
USING ( select c.id, c.name, cd.date,
cd.population, cd.urban_pop, cd.birthrate,
cf.gdp, cf.gdp_per_capita
from Countries c, country_demographics cd, country_financials cf
where c.id = cd.id
and cd.id = cf.id ) a
ON (nt.id = a.id )
WHEN MATCHED THEN
UPDATE SET nt.Name = a.Name,
nt.date = a.date,
nt.population = a.population,
nt.urban_pop = a.urban_pop,
nt.birth_rate = a.birth_rate,
nt.gdp = a.gdp,
nt.gdp_per_capita = a.gdp_per_capita
WHEN NOT MATCHED THEN
INSERT (ID, Name, date, population, urban_pop, birth_rate, gdp, gdp_per_capita)
VALUES (a.id, a.Name, a.date, a.population, a.urban_pop, a.birth_rate, a.gdp, a.gdp_per_capita);

Time Difference between query result rows in SQLite: How To?

Consider the following reviews table contents:
CustomerName ReviewDT
Doe,John 2011-06-20 10:13:24
Doe,John 2011-06-20 10:54:45
Doe,John 2011-06-20 11:36:34
Doe,Janie 2011-06-20 05:15:12
The results are ordered by ReviewDT and grouped by CustomerName, such as:
SELECT
CustomerName,
ReviewDT
FROM
Reviews
WHERE
CustomerName NOT NULL
ORDER BY CustomerName ASC, ReviewDT ASC;
I'd like to create a column of the time difference between each row of this query for each Customer... rowid gives the original row, and there is no pattern to the inclusion from the rowid etc...
For the 1st entry for a CustomerName, the value would be 0. I am asking here incase this is something that can be calculated as part of the original query somehow. If not, I was planning to do this by a series of queries - initially creating a new TABLE selecting the results of the query above - then ALTERING to add the new column and using UPDATE/strftime to get the time differences by using rowid-1 (somehow)...
To compute the seconds elapsed from one ReviewDT row to the next:
SELECT q.CustomerName, q.ReviewDT,
strftime('%s',q.ReviewDT)
- strftime('%s',coalesce((select r.ReviewDT from Reviews as r
where r.CustomerName = q.CustomerName
and r.ReviewDT < q.ReviewDT
order by r.ReviewDT DESC limit 1),
q.ReviewDT))
FROM Reviews as q WHERE q.CustomerName NOT NULL
ORDER BY q.CustomerName ASC, q.ReviewDT ASC;
To get the DT of each ReviewDT and its preceding CustomerName row:
SELECT q.CustomerName, q.ReviewDT,
coalesce((select r.ReviewDT from Reviews as r
where r.CustomerName = q.CustomerName
and r.ReviewDT < q.ReviewDT
order by r.ReviewDT DESC limit 1),
q.ReviewDT)
FROM Reviews as q WHERE q.CustomerName NOT NULL
ORDER BY q.CustomerName ASC, q.ReviewDT ASC;

Resources