I need to respect this Business Rule: Set EXPIRATION_DATE NULL if the TENANT is an OWNER of the APARTMENT. EXPIRATION_DATE indicates the expiry date of a rental contract
TENANT (COD_T, EXPIRATION_DATE, COD_APARTMENT) --where the tenant is living
OWNER (COD_O, COD_APARTMENT) --apartments that belong to the owner
APARTMENT (COD_APARTMENT)
I'd like to know: if I use this script and the CHECK became true, it will set automatically EXPIRATION_DATE to NULL?
If not, how can I do it?
CREATE TABLE TENANT(
COD_T CHAR(5) PRIMARY KEY,
COD_APARTMENT INT REFERENCES APARTMENT(COD_APARTMENT),
EXPIRATION_DATE DATE
(CHECK (COD_T IN ( SELECT COD_O -- same type COD_T
FROM OWNER O
WHERE COD_APARTMENT = O.CODAPARTMENT
)
)
AND EXPIRATION_DATE IS NULL
);
You can use a view do get the data in your required check constraint format
CREATE OR replace VIEW tenant_vw
AS
SELECT cod_t,
cod_apartment,
CASE
WHEN cod_t IN (SELECT cod_o -- same type COD_T
FROM owner O
WHERE cod_apartment = O.codapartment) THEN NULL
ELSE expiration_date
END AS EXPIRATION_DATE
FROM tenant;
You can use the view for such requirement but if you want your data to be updated like this then you need to create the trigger as follows:
CREATE TRIGGER TRG_TENANT
BEFORE INSERT OR UPDATE ON TENANT
FOR EACH ROW
DECLARE
CNT NUMBER;
BEGIN
SELECT COUNT(1)
INTO CNT
FROM OWNER O
WHERE O.CODAPARTMENT = :NEW.COD_APARTMENT
AND O.COD_O = :NEW.COD_T;
IF CNT > 0 THEN
:NEW.EXPIRATION_DATE := NULL;
END IF;
END;
/
Related
I am currently working under postgres 14.
I got two tables customers and contacts, and i want to automatically find the customer_id from the customer name when i add a new contact in the table contacts.
CREATE TABLE customers(
customer_id INT GENERATED ALWAYS AS IDENTITY,
customer_name VARCHAR(255) NOT NULL UNIQUE,
PRIMARY KEY(customer_id)
);
CREATE TABLE contacts(
contact_id INT GENERATED ALWAYS AS IDENTITY,
customer_id INT,
contact_name VARCHAR(255) NOT NULL UNIQUE,
PRIMARY KEY(contact_id),
CONSTRAINT fk_customer
FOREIGN KEY(customer_id)
REFERENCES customers(customer_id)
);
INSERT INTO customers(customer_name) VALUES('my_first_customer')
So from here i want to do something like that :
INSERT INTO contacts(customer_id, contact_name ) VALUES('my_first_customer',"thomas")
and i want to get this result in contacts table :
contact_id
customer_id
contact_name
1
1
"thomas"
i tried to make a function to change the value from name to id but get an error of type.
Because the the type error is catch before the trigger. Here is my function
CREATE FUNCTION get_id_fct()
RETURNS TRIGGER AS $get_id_fct$
DECLARE val_id INTEGER;
BEGIN
SELECT customer_id INTO val_id FROM customers WHERE customers.customer_id = NEW.customer_id;
NEW.customer_id := val_id;
RETURN NEW
END
$get_id_fct$ LANGUAGE plpgsql;
CREATE TRIGGER get_id
BEFORE INSERT ON contacts
FOR EACH ROW EXECUTE PROCEDURE get_id_fct();'
Is their a way around that ? or specific method to do this task that i don't know about ?
I am quite a beginner at SQL.
You can make a subquery in insert statement
INSERT INTO contacts(customer_id, contact_name ) VALUES (
(select customer_id from customers where customer_name = 'my_first_customer') ,'thomas');
This query will fail if there is more than one customer with given name, and insert a null value for customer_id if there is no customers with given name
Different approach (proposed by #wildplasser)
INSERT INTO contacts(customer_id, contact_name )
select customer_id,'thomas' from customers where customer_name = 'my_first_customer';
In this case, when there is no customer with given name, no row will be created. When there is more than one customer with given name, for each of them record will be created.
Or you can create view with INSTEAD OF trigger.
create view v_contacts as
select customer_name, contact_name from customers
join contacts on customers.customer_id = contacts.customer_id;
CREATE FUNCTION emp () RETURNS trigger AS $$
BEGIN
INSERT INTO contacts(customer_id, contact_name )
VALUES((select customer_id from customers where customer_name =
NEW.customer_NAME),NEW.contact_NAME);
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER v_contactst
INSTEAD OF INSERT ON v_contacts
FOR EACH ROW
EXECUTE FUNCTION emp();
Insert statement
INSERT INTO v_contacts(customer_name, contact_name ) VALUES('my_first_customer','thomas')
And just a note, that columns customer_name and contact_name are not unique so this code is not safe and throw error if customer_name didn't exists or there is more than one record with this customer_name
I need to create a procedure to treat this case in the most performative way possible (is an extremely large amount of data).
I have a table called ORDER_A that every day receives a full load (its truncated, and all records are inserted again).
I have a table called ORDER_B which is a copy of ORDER_A, containing the same data and some additional control dates.
I also have a table MANAGER to save start and finish date, and if the procedure is running.
After all inserts are done in ORDER_A, i want to execute a procedure that, for each record on ORDER_A, must looks for a record with the same identifier (primary key: order_id) in table B.
If a record exists with the same order_id, and any of the other columns have changed, an update must be performed on table B
If a record exists with the same order_id, and no values in the other columns have been modified, nothing should be performed, the record must remain the same in table B.
If there is no record with the same order_id, it must be inserted in table B.
If there is a record on ORDER_B that no longer exists on ORDER_A (it was deleted), the column "flag_deleted" must be updated to "1".
My tables are like this
CREATE TABLE ORDER_A
(
ORDER_ID NUMBER NOT NULL,
ORDER_CODE VARCHAR2(50),
ORDER_STATUS VARCHAR2(20),
ORDER_USER_ID NUMBER,
ORDER_DATE TIMESTAMP(6),
CHECKSUM_CODE VARCHAR2(40),
PRIMARY KEY (ORDER_ID)
);
CREATE TABLE ORDER_B
(
ORDER_ID NUMBER NOT NULL,
ORDER_CODE VARCHAR2(50),
ORDER_STATUS VARCHAR2(20),
ORDER_USER_ID NUMBER,
ORDER_DATE TIMESTAMP(6)
INSERT_AT TIMESTAMP(6) DEFAULT CURRENT_TIMESTAMP,
UPDATED_AT TIMESTAMP(6),
CHECKSUM_CODE VARCHAR2(40),
FLAG_DELETED NUMBER(1),
PRIMARY KEY (ORDER_ID)
);
-- index on checksum column for both tables
CREATE INDEX idx_cksum on ORDER_A (CHECKSUM_CODE ASC);
CREATE INDEX idx_cksum on ORDER_B (CHECKSUM_CODE ASC);
-- Manager table
CREATE TABLE MANAGER
(
TABLE_NAME VARCHAR2(40),
PROCEDURE_NAME VARCHAR2(50),
START_TS TIMESTAMP(6),
FINISH_TS TIMESTAMP(6),
IS_RUNNING NUMBER(1)
);
I'm thinking in something like this procedure below, but I'm not sure if it's the best way and how to deal with the delete case
create or replace procedure MERGE_DATA_ORDER
DECLARE
is_running number;
ex_running EXCEPTION;
BEGIN
SELECT IS_RUNNING INTO is_running FROM MANAGER WHERE PROCEDURE_NAME = 'MERGE_DATA_ORDER';
IF is_running = 1
then RAISE ex_running
ELSE
-- Update the flag on manager table
UPDATE MANAGER SET IS_RUNNING = 1, START_TS = SYSTIMESTAMP WHERE PROCEDURE_NAME = 'MERGE_DATA_ORDER';
COMMIT;
-- update all records with a checksum using STANDARD_HASH with MD5
UPDATE ORDER_A
SET CHECKSUM_CODE =
STANDARD_HASH
(
ORDER_ID ||
ORDER_CODE ||
ORDER_STATUS ||
ORDER_USER_ID ||
ORDER_DATE,
'MD5'
);
COMMIT;
-- then, I do a MERGE operation, using the checksum as a comparator
merge into ORDER_B b
using (select a.* from ORDER_A a) m
on (m.ORDER_ID = b.ORDER_ID)
when matched then
update
set
b.ORDER_ID = m.ORDER_ID,
b.ORDER_CODE = m.ORDER_CODE,
b.ORDER_STATUS = m.ORDER_STATUS,
b.ORDER_USER_ID = m.ORDER_USER_ID,
b.ORDER_DATE = m.ORDER_DATE,
b.COD_CHECKSUM = m.COD_CHECKSUM,
b.DAT_UPDATE = SYSTIMESTAMP
where b.CHECKSUM_CODE <> m.CHECKSUM_CODE
when not matched then
insert (
b.ORDER_ID,
b.ORDER_CODE,
b.ORDER_STATUS,
b.ORDER_USER_ID,
b.ORDER_DATE,
b.COD_CHECKSUM
)
values (
m.ORDER_ID,
m.ORDER_CODE,
m.ORDER_STATUS,
m.ORDER_USER_ID,
m.ORDER_DATE,
m.COD_CHECKSUM
);
END IF;
-- set the flag to 0
UPDATE MANAGER SET IS_RUNNING = 0, FINISH_TS = SYSTIMESTAMP WHERE PROCEDURE_NAME = 'MERGE_DATA_ORDER';
COMMIT;
END;
/
I need some help to complete this code, performance tips and deal with the delete issue;
I think you can do this as a single statement as part of the data load. Let's assume that ORDER_A has been loaded (but I will comment on that later). Then you can define the result of the insert/update by doing a full outer join between ORDER_A and ORDER_B, and the use a CASE statement to project the "correct" value from ORDER_A or ORDER_B. Similarly you can project the FLAG_DELTED. It would look something like this. In this example, I am skipping the MD5, but this could be added if really needed - more on that later too
select
case
when ( b.order_id is null ) then a.order_id
else case when (
b.ORDER_ID != m.ORDER_ID or
b.ORDER_CODE != m.ORDER_CODE or
b.ORDER_STATUS != m.ORDER_STATUS or
b.ORDER_USER_ID != m.ORDER_USER_ID or
b.ORDER_DATE != m.ORDER_DATE or
b.DAT_UPDATE != SYSTIMESTAMP ) then b.order_id else a.order_id end
end as newOrder_id
, case when ( b.order_id is null ) then a.order_code
else case when (
b.ORDER_ID != m.ORDER_ID or
b.ORDER_CODE != m.ORDER_CODE or
b.ORDER_STATUS != m.ORDER_STATUS or
b.ORDER_USER_ID != m.ORDER_USER_ID or
b.ORDER_DATE != m.ORDER_DATE or
b.DAT_UPDATE != SYSTIMESTAMP ) then b.order_code else a.order_code end
end as newOrder_code
, case when ( b.order_id is null ) then a.order_status
else case when (
b.ORDER_ID != m.ORDER_ID or
b.ORDER_CODE != m.ORDER_CODE or
b.ORDER_STATUS != m.ORDER_STATUS or
b.ORDER_USER_ID != m.ORDER_USER_ID or
b.ORDER_DATE != m.ORDER_DATE or
b.DAT_UPDATE != SYSTIMESTAMP ) then b.order_status else a.order_status end
end as newOrder_status
/* etc... ( Repeat for all projected columns )
Then for the flag_deleted column */
, case when ( a.order_id is null ) then 1
when ( b.order_id is null ) then 0
else b.flag_deleted
end as newFlag_deleted
from Order_b b
full outer join Order_a a
on b.order_id = a.order_id
It may be possible that ORDER_A could be an external table, so then you would just need to prepend this with a
CREATE TABLE NEW_ORDER_A as select....
And then you have the results you need.
Where you a hemorrhaging performance in your example, is the update of ORDER_A. You are generating redo, undo and losing any compression benefits. You are also maintaining indexes, but indexes are not needed.
Assuming you have resources, you cab now use DIRECT PATH and parallelism, and this would scale pretty well.
Lastly, if you really do need the MD5, you need to add a special character between each column, otherwise is will be ambiguous. For example, the following woukd have the same MD5
COL1 COL2
AA BBB
AAB BB
I created this table for my database.
CREATE TABLE Reservation
(
Reservation_Name SERIAL UNIQUE PRIMARY KEY,
User VARCHAR(64) DEFAULT 'Member', FOREIGN KEY(User) REFERENCES User(Email)
ON UPDATE CASCADE
ON DELETE SET DEFAULT,
Location INT, FOREIGN KEY(Location) REFERENCES Place(Id_Location)
ON UPDATE CASCADE
ON DELETE NO ACTION,
Start_Date DATE NOT NULL,
Check_In TIME(1) DEFAULT '10:00:00',
End_Date DATE NOT NULL,
Check_Out TIME(1) DEFAULT '18:00:00',
CHECK(Start_Date >= End_Date),
Deleted BOOLEAN DEFAULT FALSE
);
How can I insert a Check that doesn't allow to add a reservation if there's already another one with the same Start_Date and the same End_Date end the same location?
You can use an exclusion constraint:
CREATE EXTENSION btree_gist;
ALTER TABLE reservation ADD EXCLUDE USING gist (
location WITH =,
daterange(start_date, end_date, '[]') WITH &&
);
The extension is required so that you can create a GiST index on an integer column, and && is the "overlaps" operator for range types.
You can symply add a constraint to the table.
Alter Table Reservations Add Constraint unique_reservation Unique(Location,StartDate,EndDate);
You will need a trigger for this. Look at the above code :
CREATE TRIGGER no_overlap
BEFORE INSERT
ON Reservation FOR EACH ROW
BEGIN
SET #overlaps = ( SELECT count(*) FROM Reservation WHERE ( ( NEW.Start_Date >= Start_Date AND NEW.Start_Date <= End_Date AND NEW.Location = Location) || ( NEW.End_Date >= Start_Date AND NEW.End_Date <= End_Date AND NEW.Location = Location)));
IF #overlaps > 0 THEN
SIGNAL SQLSTATE '45000' SET
MYSQL_ERRNO = 31000,
MESSAGE_TEXT = 'Unable to insert an overlapping reservation';
END IF;
END;
INSERT INTO Reservation (Location,Start_Date,End_Date) VALUES(1,'2020-12-13','2020-12-16');
INSERT INTO Reservation (Location,Start_Date,End_Date) VALUES(1,'2020-12-14','2020-12-17');
The first insert will succeed while the second one will fail with the corresponding error message if the dates overlap :
SQL Error [31000] [45000]: (conn=10) Unable to insert an overlapping reservation
By the way, I think you have an error in your table definition. Instead of CHECK(Start_Date >= End_Date), I think you meant CHECK(Start_Date <= End_Date),
Let me know if it helps.
Note : I did this on MariaDB but you can apply the same for any SQL DB.
This works in sql server. I don't have access at the moment to check against postgres. You will need to run in two different batches after creating your table
First
CREATE FUNCTION dbo.HasOverlap (
#locationId int, #start datetime, #end datetime)
RETURNS VARCHAR(5)
AS
BEGIN
IF (SELECT count(*) FROM dbo.Reservation WHERE Location = #locationId
and (
#start between Start_Date and End_Date
or
#end between Start_Date and End_Date
or
(#start <=Start_Date and #end>=End_Date )
)
) >1
return 1
return 0
END
Second
Alter Table dbo.Reservation
with check add Constraint Check_Overlap
check (dbo.HasOverlap(Location, Start_Date, End_Date)=0)
You need to use the composite primary key concept in MySQL Database. Its disable to insert duplicate items in specific columns.
ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (Start_Date, End_Date, Location)
I am implementing a library management system in SQL. I have the following table structure and some values inserted in them:
create table books
(
IdBook number(5),
NameBook varchar2(35),
primary key(IdBook)
);
create table users
(
IdUsers number(5),
NameUser varchar2(20),
primary key(IdUsers)
);
create table borrowed
(
IdBorrowed number(5),
IdUsers number(5),
IdBook number(5),
DueDate date,
DateReturned date,
constraint fk_borrowed foreign key(IdUsers) references users(IdUsers),
constraint fk_borrowed2 foreign key(IdBook) references books(IdBook)
);
insert into books values(0,'FairyTale');
insert into books values(1,'Crime and Punishment');
insert into books values(2,'Anna Karenina');
insert into books values(3,'Norwegian Wood');
insert into users values(01,'Robb Dora');
insert into users values(02,'Pop Alina');
insert into users values(03,'Grozavescu Teodor');
insert into users values(04,'Popa Alin');
insert into borrowed values(10,02,3,'22-Jan-2017',null);
insert into borrowed values(11,01,1,'25-Jan-2017','19-Dec-2016');
insert into borrowed values(12,01,3,'22-Jan-2017',null);
insert into borrowed values(13,04,2,'22-Jan-2017','13-Dec-2016');
What I want now is that my db to allow "borrowing" books for the users(i.e insert into the borrowed table) that have no unreturned books(i.e date returned is not null) and if they have unreturned books I want to abandon the whole process. I thought to implement this in the following way:
create or replace procedure borrowBook(IdBorrowed in number,IdUsers number,IdBook number,DueDate date,DateReturned date) as begin
if exists (SELECT u.IdUsers, u.NameUser, b.DateReturned
FROM users u, borrowed b
WHERE u.IDUSERS = b.IdUsers and DateReturned is not null),
insert into borrowed values(IdBorrowed,IdUsers,IdBook,DueDate,DateReturned);
end borrowBook;
The above procedure does not check if the parameter I pass to this function is the same as the one in my select and I do not know how to do this and correctly insert a value in my table.
Any help would be much appreciated. Thank in advance!
You should not name your parameters the same as columns also used inside the procedure.
You can also simplify your procedure to a single INSERT statement, no IF required:
create or replace procedure borrowBook(p_idborrowed in number, p_idusers number, p_idbook number, p_duedate date, p_datereturned date)
as
begin
insert into borrowed (idborrowed, idusers, idbook, duedate, datereturned)
select p_idborrowed, p_idusers, p_idbook, p_duedate, p_datereturned
from dual
where not exists (select *
from users u
join borrowed b on u.idusers = b.idusers
and b.datereturned is not null);
end borrowBook;
It's also good coding style to explicitly list the columns for an INSERT statement. And you should get used to the explicit JOIN operator instead of using implicit joins in the where clause.
What about this one:
create or replace procedure borrowBook( p_IdBorrowed in number ,
p_IdUsers number ,
p_IdBook number ,
p_DueDate date ,
p_DateReturned date )
as
begin
if (SELECT COUNT(*)
FROM borrowed
WHERE IDUSERS = p_IdUsers
AND DateReturned IS NULL) = 0 THEN
insert into borrowed values (p_IdBorrowed ,
p_IdUsers ,
p_IdBook ,
p_DueDate ,
p_DateReturned );
end if ;
end borrowBook;
You would seem to want something like this:
create or replace procedure borrowBook (
in_IdBorrowed in number,
in_IdUsers number,
in_IdBook number,
in_DueDate date,
in_DateReturned date
) as
v_flag number;
begin
select (case when exists (select 1
from borrowed b
where b.IdUsers = in_IdUsers and b.DateReturned is not null
)
then 1 else 0
end)
into v_flag
from dual;
if (flag = 0) then
insert into borrowed
values(in_IdBorrowed, in_IdUsers, in_IdBook, in_DueDate, v_DateReturned);
end if
end -- borrowBook;
I have a small little thing with SQL that's been bothering me now for a while, let's say I have two tables (Customer and Loan). However, I want a trigger that's checking based on the Borrowertype attribute. I suppose with the second query after AND I need something to check whether the userID in Loans are the same as the one in Customer, but must be messing it up or I'm completely thinking this the wrong way.
CREATE TABLE Customer
(
userID int identity primary key,
Name varchar(20),
Borrowertype varchar(20)
);
CREATE TABLE Loan
(
Id int identity primary key,
userID int,
FOREIGN KEY (userID) REFERENCES Customer(userID)
);
IF OBJECT_ID ('Customer.maximum_books_per_user','TR') IS NOT NULL
DROP TRIGGER Customer.maximum_books_per_user;
GO
CREATE TRIGGER maximum_books_per_user ON Customer
AFTER INSERT
AS
IF (SELECT Borrowertype FROM Customer) = 'diffborrowertypehere'
AND (SELECT COUNT(*) FROM inserted AS i JOIN Customer AS c
ON ??? WHERE ???
) > 5
BEGIN
ROLLBACK TRANSACTION
RAISERROR('You have reached maximum allowed loans.', 16, 1)
END
GO
Your trigger needs to be on the Loan table, as that's where a row would be being inserted that could be rejected. Something like this:
EDIT: rewritten to handle inserts for multiple Customers at once
CREATE TRIGGER maximum_books_per_user ON Loan
FOR INSERT
AS
-- Fail if there are any customers that will have more than the maximum number of loans
IF EXISTS (
SELECT i.userID, COUNT(*)
FROM inserted i
JOIN Loan l
ON i.userID = l.userID
GROUP BY i.userID
HAVING COUNT(*) >= 5
)
BEGIN
ROLLBACK TRANSACTION
RAISERROR('You have reached maximum allowed loans.', 16, 1)
END