I'm running MariaDB 10.3.17 and I'm trying to add a constraint to an existing table. The constraint uses a UDF - which should be allowed.
Here's my table and UDF.
CREATE OR REPLACE TABLE real_estate.sample_two_expected_output (
u_id int (9) NOT NULL,
first_date date NOT NULL,
last_date date NOT NULL,
days int AS (DATEDIFF(last_date,first_date)+1),
address varchar(50),
price varchar(50),
--Constraints
CONSTRAINT dates CHECK (last_date >= first_date),
PRIMARY KEY (u_id,first_date));
DELIMITER //
USE real_estate;
CREATE OR REPLACE FUNCTION overlap(
u_id INT,
first_date DATE,
last_date DATE
) RETURNS INT DETERMINISTIC
BEGIN
DECLARE valid INT;
SET valid = 1;
IF EXISTS(SELECT * FROM real_estate.sample_two_expected_output t WHERE t.u_id = u_id AND first_date <= t.last_date AND t.first_date <= last_date) THEN SET valid = 0;
ELSE SET valid = 1;
END IF;
RETURN valid;
END; \\
DELIMITER;
I try to add this function as a constraint in the table.
ALTER TABLE real_estate.sample_two_expected_output ADD CONSTRAINT overlap CHECK(overlap(u_id,first_date,last_date)=1);
However I get the below error message and I don't know why.
EXECUTE FAIL:
ALTER TABLE real_estate.sample_two_expected_output ADD CONSTRAINT overlap CHECK(overlap(u_id,first_date,last_date)=1);
Message :
Function or expression '`overlap`()' cannot be used in the CHECK clause of `overlap`
In general you can use any deterministic user defined function (UDF) but not a stored function (SF) in constraints like DEFAULT, CHECK, etc.
A big difference between UDFs and SFs is the fact that a UDF is usually written in C/C++ while a SF is written in SQL. That means it is not possible to execute SQL code in a UDF within the same connection, which would lead to significant problems, as your SF shows:
Depending on the storage engine ALTER TABLE locks the entire table, parts of it or creates a temporary copy. I cannot imagine a way to execute the SQL statement SELECT * FROM real_estate.sample_two_expected_output t WHERE t.u_id = u_id .. in your SF while the table is locked or reorganized.
Related
Is it possible to have a Constraint but only when one column is set to a particular value. For example take this pseudo-code example of a President which checks to make sure there is never more than 1 President at any time (note, this is NOT valid psql syntax)
CREATE TABLE president (
id BIGSERIAL PRIMARY KEY,
current BOOLEAN NOT NULL,
CONSTRAINT there_can_be_only_one CHECK(COUNT(current=true)<=1)
);
You can use the so called partial index to enforce this specific constraint. In SQL Server they are called filtered indexes.
CREATE UNIQUE INDEX IX ON president (current)
WHERE current = true;
This index should prevent having more than one row in a table with current value set to true, because it is defined as unique.
Unfortunately NO as far as I know and anyway it already tells us,
ERROR: aggregate functions are not allowed in check constraints.
But we can use BEFORE trigger to check that the data you are trying to insert should meets the criteria COUNT(current=true)<=1
CREATE TABLE president (
id BIGSERIAL PRIMARY KEY,
current BOOLEAN NOT NULL
);
---------------------------------------------------------------------
CREATE FUNCTION check_current_flag()
RETURNS trigger
AS $current_president$
DECLARE
current_flag_count integer;
BEGIN
SELECT COUNT(*) FILTER (WHERE current = true )
INTO current_flag_count
FROM president;
IF new.current = true
and current_flag_count >= 1 THEN
RAISE EXCEPTION 'There can be only one current president';
-- RETURN NULL;
ELSE
RETURN NEW;
END IF;
END;
$current_president$ LANGUAGE plpgsql;
---------------------------------------------------------------------
CREATE TRIGGER current_president BEFORE INSERT OR UPDATE ON president
FOR EACH ROW EXECUTE PROCEDURE check_current_flag();
Db<>Fiddle for reference
Note:
You can either throw exception in case of preconditions doesn't match ore simply returning NULL will skip the insert and do nothing. as official document says also here
First here's the relevant code:
create table customer(
customer_mail_address varchar(255) not null,
subscription_start date not null,
subscription_end date, check (subscription_end !< subcription start)
constraint pk_customer primary key (customer_mail_address)
)
create table watchhistory(
customer_mail_address varchar(255) not null,
watch_date date not null,
constraint pk_watchhistory primary key (movie_id, customer_mail_address, watch_date)
)
alter table watchhistory
add constraint fk_watchhistory_ref_customer foreign key (customer_mail_address)
references customer (customer_mail_address)
on update cascade
on delete no action
go
So i want to use a UDF to constrain the watch_date in watchhistory between the subscription_start and subscription_end in customer. I can't seem to figure it out.
Check constraints can't validate data against other tables, the docs say (emphasis mine):
[ CONSTRAINT constraint_name ]
{
...
CHECK [ NOT FOR REPLICATION ] ( logical_expression )
}
logical_expression
Is a logical expression used in a CHECK constraint and returns TRUE or
FALSE. logical_expression used with CHECK constraints cannot
reference another table but can reference other columns in the same
table for the same row. The expression cannot reference an alias data
type.
That being said, you can create a scalar function that validates your date, and use the scalar function on the check condition instead:
CREATE FUNCTION dbo.ufnValidateWatchDate (
#WatchDate DATE,
#CustomerMailAddress VARCHAR(255))
RETURNS BIT
AS
BEGIN
IF EXISTS (
SELECT
'supplied watch date is between subscription start and end'
FROM
customer AS C
WHERE
C.customer_mail_address = #CustomerMailAddress AND
#WatchDate BETWEEN C.subscription_start AND C.subscription_end)
BEGIN
RETURN 1
END
RETURN 0
END
Now add your check constraint so it validates that the result of the function is 1:
ALTER TABLE watchhistory
ADD CONSTRAINT CHK_watchhistory_ValidWatchDate
CHECK (dbo.ufnValidateWatchDate(watch_date, customer_mail_address) = 1)
This is not a direct link to the other table, but a workaround you can do to validate the date. Keep in mind that if you update the customer dates after the watchdate insert, dates will be inconsistent. The only way to ensure full consistency in this case would be with a few triggers.
I would like to add a constraint that will check values from related table.
I have 3 tables:
CREATE TABLE somethink_usr_rel (
user_id BIGINT NOT NULL,
stomethink_id BIGINT NOT NULL
);
CREATE TABLE usr (
id BIGINT NOT NULL,
role_id BIGINT NOT NULL
);
CREATE TABLE role (
id BIGINT NOT NULL,
type BIGINT NOT NULL
);
(If you want me to put constraint with FK let me know.)
I want to add a constraint to somethink_usr_rel that checks type in role ("two tables away"), e.g.:
ALTER TABLE somethink_usr_rel
ADD CONSTRAINT CH_sm_usr_type_check
CHECK (usr.role.type = 'SOME_ENUM');
I tried to do this with JOINs but didn't succeed. Any idea how to achieve it?
CHECK constraints cannot currently reference other tables. The manual:
Currently, CHECK expressions cannot contain subqueries nor refer to
variables other than columns of the current row.
One way is to use a trigger like demonstrated by #Wolph.
A clean solution without triggers: add redundant columns and include them in FOREIGN KEY constraints, which are the first choice to enforce referential integrity. Related answer on dba.SE with detailed instructions:
Enforcing constraints “two tables away”
Another option would be to "fake" an IMMUTABLE function doing the check and use that in a CHECK constraint. Postgres will allow this, but be aware of possible caveats. Best make that a NOT VALID constraint. See:
Disable all constraints and table checks while restoring a dump
A CHECK constraint is not an option if you need joins. You can create a trigger which raises an error instead.
Have a look at this example: http://www.postgresql.org/docs/9.1/static/plpgsql-trigger.html#PLPGSQL-TRIGGER-EXAMPLE
CREATE TABLE emp (
empname text,
salary integer,
last_date timestamp,
last_user text
);
CREATE FUNCTION emp_stamp() RETURNS trigger AS $emp_stamp$
BEGIN
-- Check that empname and salary are given
IF NEW.empname IS NULL THEN
RAISE EXCEPTION 'empname cannot be null';
END IF;
IF NEW.salary IS NULL THEN
RAISE EXCEPTION '% cannot have null salary', NEW.empname;
END IF;
-- Who works for us when she must pay for it?
IF NEW.salary < 0 THEN
RAISE EXCEPTION '% cannot have a negative salary', NEW.empname;
END IF;
-- Remember who changed the payroll when
NEW.last_date := current_timestamp;
NEW.last_user := current_user;
RETURN NEW;
END;
$emp_stamp$ LANGUAGE plpgsql;
CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp
FOR EACH ROW EXECUTE PROCEDURE emp_stamp();
...i did it so (nazwa=user name, firma = company name) :
CREATE TABLE users
(
id bigserial CONSTRAINT firstkey PRIMARY KEY,
nazwa character varying(20),
firma character varying(50)
);
CREATE TABLE test
(
id bigserial CONSTRAINT firstkey PRIMARY KEY,
firma character varying(50),
towar character varying(20),
nazwisko character varying(20)
);
ALTER TABLE public.test ENABLE ROW LEVEL SECURITY;
CREATE OR REPLACE FUNCTION whoIAM3() RETURNS varchar(50) as $$
declare
result varchar(50);
BEGIN
select into result users.firma from users where users.nazwa = current_user;
return result;
END;
$$ LANGUAGE plpgsql;
CREATE POLICY user_policy ON public.test
USING (firma = whoIAM3());
CREATE FUNCTION test_trigger_function()
RETURNS trigger AS $$
BEGIN
NEW.firma:=whoIam3();
return NEW;
END
$$ LANGUAGE 'plpgsql'
CREATE TRIGGER test_trigger_insert BEFORE INSERT ON test FOR EACH ROW EXECUTE PROCEDURE test_trigger_function();
So for now, I created 2 tables, Booking and BookingDetails, I want to create a trigger when I key in the details of BookingDetails it will automatically update totaldays inside the Booking table. Below is my code:
BookingDetails:
create table BookingDetail (
BD_ID int primary key not null,
Date_In date,
Date_Out date,
BK_ID int,
Room_ID int,
foreign key(BK_ID) references Booking(BK_ID),
foreign key(Room_ID) references Room(Room_ID)
)
And also Booking
create table Booking (
BK_ID int primary key not null,
BK_Date Date,
BK_TotalDays int,
BK_PayStatus char(6),
Cus_ID int,
Emp_ID int,
foreign key(Cus_ID) references customer(Cus_ID),
foreign key(Emp_ID) references Employee(Emp_ID)
)
With the function and trigger created:
create function countdays(t1 date, t2 date)
returns INT
return (timestampdiff(16, char(timestamp(t2) - timestamp(t1))))
create trigger totaldays
after insert on bookingdetail
referencing new as n
for each row mode db2sql
update booking
set bk_totaldays =
countdays((select date_in from bookingdetail), (select date_out from
bookingdetail))
where booking.bk_id = n.bk_id;
I have no problem executing these syntax, but when I try to input a new record inside Booking Detail to let the trigger triggers in Booking, errors occured, may I ask why? Thanks in advance.
Look at the information provided by the SQL error:
db2 ? SQL0811
SQL0811N The result of a scalar fullselect, SELECT INTO statement, or
VALUES INTO statement is more than one row.
So this part of your trigger expressions returns more than 1 row
set bk_totaldays = countdays((select date_in from bookingdetail),
(select date_out from bookingdetail))
Fix this to return a single row.
#MichaleTiefenbacher is correct about the cause of the error, but he's wrong about what to do about it. Let's take another look at your trigger again:
create trigger totaldays
after insert on bookingdetail
referencing new as n -- wait, what's this?
for each row mode db2sql
update booking
set bk_totaldays =
countdays((select date_in from bookingdetail), (select date_out from bookingdetail))
where booking.bk_id = n.bk_id;
You have a reference to the value you just inserted! When using FOR EACH ROW, the table reference NEW refers to the singular row just inserted. So you don't even need to look at the full table, just use what you just worked with:
create trigger totaldays
after insert on bookingdetail
referencing new as n
for each row mode db2sql
update booking
set bk_totaldays = countdays(n.date_in, n.date_out)
where booking.bk_id = n.bk_id;
(As I mentioned in my comment to your question, you'll likely want to change how you calculate the days, but that's irrelevant for this)
This question already has answers here:
Set ORACLE table fields default value to a formular
(2 answers)
Closed 8 years ago.
I got a table which I used the below code to create.
create table Meter (MeterID CHAR(8) CONSTRAINT MeterPK PRIMARY KEY,
Value CHAR(8) CONSTRAINT ValueNN NOT NULL,
InstalledDate Date CONSTRAINT InDateNN NOT NULL);
Then I tried adding a derived column that adds 6 months to the installeddate.
alter table meter add ExpiryDate as (add_months(installedDate,6)) not null;
This returns an error of invalid datatype.
I read somewhere that I do not have to specify the datatype of ExpiryDate as it can be derived from the function. So where did I go wrong?
EDIT: Turns out Mike was right. I used the trigger method to get things going, but I was confused whether I'm using mysql or oracle. Think in the end I'm using oracle actually. Have problems with the trigger but turns out I do not need to have the command "set" in the trigger. Below is the code that works.
CREATE OR REPLACE
TRIGGER trigexpdate1
BEFORE INSERT ON Meter
FOR EACH ROW
BEGIN
:NEW.ExpiryDate := ADD_MONTHS(:NEW.InstalledDate, 6);
END;
If I don't have the begin and end in the statement, it will throw an error saying illegal trigger specification.
MySQL doesn't support
derived columns in table definitions,
a function named add_months(), or
inline constraints.
This is a more or less standard way to write that statement in MySQL.
create table `Meter` (
`MeterID` CHAR(8) NOT NULL,
`Value` CHAR(8) NOT NULL,
`InstalledDate` Date NOT NULL,
primary key (`MeterID`)
);
You have two options for a derived column like "ExpiryDate".
Create a view, and do the date arithmetic in the view. Use date_add().
Add the column "ExpiryDate" to the table, and keep it up-to-date with a trigger.
BEFORE INSERT trigger example
create table `Meter` (
`MeterID` CHAR(8) NOT NULL,
`Value` CHAR(8) NOT NULL,
`InstalledDate` Date NOT NULL,
`ExpiryDate` Date not null,
primary key (`MeterID`)
);
create trigger trigexpdate1
before insert on `Meter`
FOR EACH ROW
SET NEW.`ExpiryDate` = date_add(NEW.`InstalledDate`, interval 6 month);
Note how ExpiryDate changes from the insert statement to the select statement below.
insert into Meter
values ('1', '1', '2014-07-01', '2014-07-01');
select * from Meter;
MeterID Value InstalledDate ExpiryDate
--
1 1 2014-07-01 2015-01-01