Related
I am created 2 tables named entry and team based on the attached logical model.
I didn't have any problems with the create table as I created the tables first. altered the table to have the primary keys. and by the end add foreign keys.
CREATE TABLE entry (
event_id NUMBER(6) NOT NULL,
entry_no NUMBER(5) NOT NULL,
entry_starttime DATE,
entry_finishtime DATE,
comp_no NUMBER(5) NOT NULL,
team_id NUMBER(3),
char_id NUMBER(3)
);
ALTER TABLE entry ADD CONSTRAINT entry_pk PRIMARY KEY ( event_id,
entry_no );
CREATE TABLE team (
team_id NUMBER(3) NOT NULL,
team_name VARCHAR(30) NOT NULL,
carn_date DATE NOT NULL,
team_no_members NUMBER(2) NOT NULL,
event_id NUMBER(6) NOT NULL,
entry_no NUMBER(5) NOT NULL,
char_id NUMBER(3)
);
ALTER TABLE team ADD CONSTRAINT team_pk PRIMARY KEY ( team_id );
ALTER TABLE team ADD CONSTRAINT team_nk UNIQUE ( team_name,
carn_date );
ALTER TABLE entry
ADD CONSTRAINT team_entry FOREIGN KEY ( team_id )
REFERENCES team ( team_id );
ALTER TABLE team
ADD CONSTRAINT entry_team FOREIGN KEY ( event_id,
entry_no )
REFERENCES entry ( event_id,
entry_no );
My problems come in when i start inserting values to the tables.
team_no is a foreign key in entry table (but could be null). event_id and entry_no are foreign keys (not null) in team table.
INSERT INTO entry (
event_id,
entry_no,
entry_starttime,
entry_finishtime,
comp_no,
team_id,
char_id
) VALUES (
6,
2,
TO_DATE('08:30', 'HH:MI'),
TO_DATE('08:50', 'HH:MI'),
10,
NULL,
1
);
INSERT INTO team (
team_id,
team_name,
carn_date,
team_no_members,
event_id,
entry_no,
char_id
) VALUES (
5,
'Turner Hall',
TO_DATE('24/SEP/2021', 'DD/MON/YYYY'),
2,
2,
1,
4
);
it gives me a ORA-02291: integrity constraint (string.string) violated - parent key not found error.
How can I fix this?
Thanks!
Fix your design first.
Start out with some simple sentences that define the what each thing is (Carnival, Event, Entry, Team, Competitor, Charity).
Once you know what they mean then you can write some more simple sentences defining the relationships.
Only once you have it straight in your head what everything is and how it is related then you can create the entity-relationship diagram and that diagram should be a visual representation that has a 1:1 correspondence to your simple sentence descriptions.
If you find you want to add a constraint in the ER diagram that does not have a description then write the simple sentence description first and think long and hard about whether what you have written makes logical sense; if it does not then do not add the relationship.
So you can start with:
There are people (Competitors).
The Competitors are grouped into multiple Teams.
Each Team can have many members (Competitors) but exactly one of those is the team leader.
There are Carnivals.
Each Carnival can host multiple competitive Events.
An Event requires an Entry from each Team.
Each Team can have multiple Entrys into different Events.
Each Team can only have one Entry into each Event.
Each Event can have multiple Entry from different teams.
Each Team supports exactly one Charity.
From that description, there is no mention of competitors and events in the same relationship so, if that was the case, then in your ER diagram there should not be any direct relationship between competitors and events; instead there are relationships from each to a team.
Similarly, the team leader relationship is from a Team to a Competitor and not to an Entry.
You may have different ideas of what the tables and relationships mean but you will find that by setting everything out in simple sentences it will force you to understand what everything means and making sure it makes sense.
Once you fix your design then you will find that you have eliminated the problem of cyclic references that prevent you from inserting data without disabling constraints.
I have a target table T1 which doesn't have a Date field. The current size is increasing rapidly. Hence I need to add a Date field and also perform table partitioning on this target table.
T1 has PRIMARY KEY (DOCID, LABID)
and has CONSTRAINT FOREIGN KEY (DOCID) REFERENCES T2
Table T2 is also complex table and has many rules in it.
T2 has PRIMARY KEY (DOCID)
My question is, as I need to partition T1. Is it possible NOT TO perform any step for T2 before T1 is partition? DBA told me that I need to partition T2 first before I touch T1??
There is no need to partition T2 before partitioning T1. Foreign key constraints do not care in the slightest bit about partitioning.
Best of luck.
You have – as proposed by others - two options. The first one is to add a redundant column DATE to the table T1 (child) and introduce the range partitioning on this column.
The second option is to use reference partitioning. Below is the simplified DDL for those options.
Range partitioning on child
create table T2_P2 /* parent */
(docid number not null,
trans_date date not null,
pad varchar2(100),
CONSTRAINT t2_p2_pk PRIMARY KEY(docid)
);
create table T1_P2 /* child */
(docid number not null,
labid number not null,
trans_date date not null, /** redundant column **/
pad varchar2(100),
CONSTRAINT t1_p2_pk PRIMARY KEY(docid, labid),
CONSTRAINT t1_p2_fk
FOREIGN KEY(docid) REFERENCES T2_P2(docid)
)
PARTITION BY RANGE(trans_date)
( PARTITION Q1_2016 VALUES LESS THAN (TO_DATE('01-APR-2016','DD-MON-YYYY'))
);
Reference partition
create table T2_RP /* parent */
(docid number not null,
trans_date date not null,
pad varchar2(100),
CONSTRAINT t2_rp_pk PRIMARY KEY(docid)
)
PARTITION BY RANGE(trans_date)
( PARTITION Q1_2016 VALUES LESS THAN (TO_DATE('01-APR-2016','DD-MON-YYYY'))
);
create table T1_RP /* child */
(docid number not null,
labid number not null,
pad varchar2(100),
CONSTRAINT t1_rp_pk PRIMARY KEY(docid, labid),
CONSTRAINT t1_rp_fk
FOREIGN KEY(docid) REFERENCES T2_RP(docid)
)
PARTITION BY REFERENCE(t1_rp_fk);
Your question is basically if the first option is possible, so the answer is YES.
To decide if the first option is preferable I’d suggest checking three criteria:
Migration
The first option requires a new DATE column in the child table that must be initialized during the migration (and of course correct maintained by the application).
Lifecycle
It could be that the lifecycle of both tables is the same (e.g. both parent and child records are kept for 7 year). In this case is preferable if both tables are partitioned (on the same key).
Access
For queries such as below you will profit from the reference partitioning (both tables are pruned - i.e. only the partitions with the accessed date are queried).
select * from T2_RP T2 join T1_RP T1 on t2.docid = t1.docid
where t2.trans_date = to_date('01012016','ddmmyyyy');
In the first option you will (probalbly) end with FTS on T2 and to get pruning on T1 you need to add predicate T2.trans_date = t1.trans_date
Having said that, I do not claim that the reference partition is superior. But I think it's worth to examine both options in your context and see which one is better.
I'm wondering is it possible to use a constraint to set the value of one column to be sum of two others. For example given the following tables:
CREATE TABLE Room (
Room_Num NUMBER(3),
Room_Band_ID NUMBER(2),
Room_Type_ID NUMBER(2),
Room_Price NUMBER(4),
PRIMARY KEY (Room_Num),
FOREIGN KEY(Room_Band_ID)
REFERENCES Room_Band(Room_Band_ID),
FOREIGN KEY(Room_Type_ID)
REFERENCES Room_Type(Room_Type_ID)
);
CREATE TABLE Booking (
Booking_ID NUMBER(10) NOT NULL,
GuestID NUMBER(4) NOT NULL,
StaffID NUMBER(2) NOT NULL,
Payment_ID NUMBER(4) NOT NULL,
Room_Num NUMBER(3) NOT NULL,
CheckInDate DATE NOT NULL,
CheckOutDate DATE NOT NULL,
Booking NUMBER(2) NOT NULL,
Price NUMBER(4),
PRIMARY KEY (Booking_ID),
FOREIGN KEY(GuestID)
REFERENCES Guest(GuestID),
FOREIGN KEY(StaffID)
REFERENCES Staff(StaffID),
FOREIGN KEY(Payment_ID)
REFERENCES Payment(Payment_ID),
FOREIGN KEY(Room_Num)
REFERENCES Room(Room_Num)
);
I know it is possible to do something like:
Constraint PriceIs CHECK (Booking.Price=(Room.Room_Price*
(Booking.CheckOutDate - Booking.CheckInDate)));
Is it also possible to set up a constraint that doesn't just ensure that the price is correct, but to calculate the price automatically into the price field for the relevant tuple?
Update,
So I've tried to set up a trigger as follows:
CREATE OR REPLACE trigger PriceCompute
AFTER INSERT ON Booking
FOR each row
BEGIN
UPDATE Booking
SET
SELECT (Room.Room_Price*(Booking.CheckOutDate - Booking.CheckInDate))
INTO
Booking.Price
FROM Booking
JOIN ROOM ON Booking.Room_Num = Room.Room_Num
END;
/
But I'm getting the following errors back:
Can anyone see where I'm going astray here, as its beyond me.
Yes, you can. Here are your options. Listed in order of my personal preference:
You can have a table without this column. And create a view that will be calculating this column on a fly.
You may use oracle virtual columns
create table Room (
...
price NUMBER GENERATED ALWAYS AS (room_price*(checkOut-checkIn)) VIRTUAL,
...)
You may use actual column (same as 2, per Dave Costa):
create table Room (
...
price AS (room_price*(checkOut-checkIn)),
...)
You can write trigger to populate it (like Mat M suggested)
You can write stored procedure, but it will be an overkill in this situation
I think you would have to put a trigger on both tables for whenever the price value of the room is changed or the checkout/in dates are changed, it will update the PriceIs field from your calculation.
If you don't need the calculated portion stored in an actual field, you can always create a view that calculates it whenever you look at the view.
I think the better solution is to use a view that calculates the value on the fly. But regarding your attempt to create a trigger, you should use :new.<column_name> to refer to the values being inserted into the Booking table. You don't need to perform updates and queries on that table to get or modify the values in the row that is being inserted*. You just refer to them as variables. So you would want to do something like:
SELECT (Room.Room_Price*(:new.CheckOutDate - :new.CheckInDate))
INTO
:new.Price
FROM ROOM WHERE :new.Room_Num = Room.Room_Num
*In fact, you can't perform queries or updates on the table whose modification invoked the trigger in the first place. You would get the infamous "mutating table" error if your trigger actually compiled and ran.
I'm working on a set of database tables in Oracle and trying to figure out a way to enforce referential integrity with slightly polymorphic data.
Specifically, I have a bunch of different tables--hypothetically, let's say I have Apples, Bananas, Oranges, Tangerines, Grapes, and a hundred more types of fruit. Now I'm trying to make a table which describes performing steps involving a fruit. So I want to insert one row that says "eat Apple ID 100", then another row which says "peel Banana ID 250", then another row which says "refrigerate Tangerine ID 500", and so on.
Historically, we've done this in two ways:
1 - Include a column for each possible type of fruit. Use a check constraint to ensure that all but one column is NULL. Use foreign keys to ensure referential integrity to our fruit. So in my hypothetical example, we'd have a table with columns ACTION, APPLEID, BANANAID, ORANGEID, TANGERINEID, and GRAPEID. For the first action, we'd have a row 'Eat', 100, NULL, NULL, NULL, NULL, NULL. For the second action, we'd have 'Peel', NULL, 250, NULL, NULL, NULL. etc. etc.
This approach is great for getting all of Oracle's RI benefits automatically, but it just doesn't scale to a hundred types of fruit. You end up getting too many columns to be practical. Just figuring out which type of fruit you are dealing with becomes a challenge.
2 - Include a column with the name of the fruit, and a column with a fruit ID. This works also, but there isn't any way (AFAIK) to have Oracle enforce the validity of the data in any way. So our columns would be ACTION, FRUITTYPE, and FRUITID. The row data would be 'Eat', 'Apple', 100, then 'Peel', 'Banana', 250, etc. But there's nothing preventing someone from deleting Apple ID 100, or inserting a step saying 'Eat', 'Apple', 90000000 even though we don't have an Apple with that ID.
Is there a way to avoid maintaining a separate column per each individual fruit type, but still preserve most the benefits of foreign keys? (Or technically, I could be convinced to use a hundred columns if I can hide the complexity with a neat trick somehow. It just has to look sane in day-to-day use.)
CLARIFICATION: In our actual logic, the "fruits" are totally disparate tables with very little commonality. Think customers, employees, meetings, rooms, buildings, asset tags, etc. The list of steps is supposed to be free-form and allow users to specify actions on any of these things. If we had one table which contained each of these unrelated things, I wouldn't have a problem, but it would also be a really weird design.
It's not clear to me why you need to identify the FRUIT_TYPE on the TASKS table. On the face of it that's just a poor (de-normalised) data model.
In my experience, the best way of modelling this sort of data is with a super-type for the generic thing (FRUIT in your example) and sub-types for the specifics (APPLE, GRAPE, BANANA). This allows us to store common attributes in one place while recording the particular attributes for each instance.
Here is the super-type table:
create table fruits
(fruit_id number not null
, fruit_type varchar2(10) not null
, constraint fruit_pk primary key (fruit_id)
, constraint fruit_uk unique (fruit_id, fruit_type)
, constraint fruit_ck check (fruit_type in ('GRAPE', 'APPLE', 'BANANA'))
)
/
FRUITS has a primary key and a compound unique key. We need the primary key for use in foreign key constraints, because compound keys are a pain in the neck. Except when they are not, which is the situation with these sub-type tables. Here we use the unique key as the reference, because by constraining the value of FRUIT_TYPE in the sub-type we can guarantee that records in the GRAPES table map to FRUITS records of type 'GRAPE', etc.
create table grapes
(fruit_id number not null
, fruit_type varchar2(10) not null default 'GRAPE'
, seedless_yn not null char(1) default 'Y'
, colour varchar2(5) not null
, constraint grape_pk primary key (fruit_id)
, constraint grape_ck check (fruit_type = 'GRAPE')
, constraint grape_fruit_fk foreign key (fruit_id, fruit_type)
references fruit (fruit_id, fruit_type)
, constraint grape_flg_ck check (seedless_yn in ('Y', 'N'))
)
/
create table apples
(fruit_id number not null
, fruit_type varchar2(10) not null
, apple_type varchar2(10) not null default 'APPLE'
, constraint apple_pk primary key (fruit_id)
, constraint apple_ck check (fruit_type = 'APPLE')
, constraint apple_fruit_fk foreign key (fruit_id, fruit_type)
references fruit (fruit_id, fruit_type)
, constraint apple_type_ck check (apple_type in ('EATING', 'COOKING', 'CIDER'))
)
/
create table bananas
(fruit_id number not null
, fruit_type varchar2(10) not null default 'BANANA'
, constraint banana_pk primary key (fruit_id)
, constraint banana_ck check (fruit_type = 'BANANA')
, constraint banana_fruit_fk foreign key (fruit_id, fruit_type)
references fruit (fruit_id, fruit_type)
)
/
In 11g we can make FRUIT_TYPE a virtual column for the sub-type and do away with the check constraint.
So, now we need a table for task types ('Peel', 'Refrigerate', 'Eat ', etc).
create table task_types
(task_code varchar2(4) not null
, task_descr varchar2(40) not null
, constraint task_type_pk primary key (task_code)
)
/
And the actual TASKS table is a simple intersection between FRUITS and TASK_TYPES.
create table tasks
(task_code varchar2(4) not null
, fruit_id number not null
, constraint task_pk primary key (task_code, fruit_id)
, constraint task_task_fk ask foreign key (task_code)
references task_types (task_code)
, constraint task_fruit_fk foreign key (fruit_id)
references fruit (fruit_id)
/
If this does not satisfy your needs please edit your question to include more information.
"... if you want different tasks for different fruits..."
Yes I wondered whether that was the motivation underlying the OP's posted design. But usually workflow is a lot more difficult than that: some tasks will apply to all fruits, some will only apply to (say) fruits which come in bunches, others will only be relevant to bananas.
"In our actual logic, the 'fruits' are totally disparate tables with
very little commonality. Think customers, employees, meetings, rooms,
buildings, asset tags, etc. The list of steps is supposed to be
free-form and allow users to specify actions on any of these things."
So you have a bunch of existing tables. You want to be able to assign records from these tables to tasks in a freewheeling style yet be able to guarantee the identify of the specific record which owns the task.
I think you still need a generic table to hold an ID for the actor in the task, but you will need to link it to the other tables somehow. Here is how I might approach it:
Soem sample existing tables:
create table customers
(cust_id number not null
, cname varchar2(100) not null
, constraint cust_pk primary key (fruit_id)
)
/
create table employees
(emp_no number not null
, ename varchar2(30) not null
, constraint emp_pk primary key (fruit_id)
)
/
A generic table to hold actors:
create table actors
(actor_id number not null
, constraint actor_pk primary key (actor_id)
)
/
Now, you need intersection tables to associate your existing tables with the new one:
create table cust_actors
(cust_id number not null
, actor_id number not null
, constraint cust_actor_pk primary key (cust_id, actor_id)
, constraint cust_actor_cust_fk foreign key (cust_id)
references customers (cust_id)
, constraint cust_actor_actor_fk foreign key (actor_id)
references actors (actor_id)
)
/
create table emp_actors
(emp_no number not null
, actor_id number not null
, constraint emp_actor_pk primary key (emp_no, actor_id)
, constraint emp_actor_emp_fk foreign key (emp_no)
references eployees (emp_no)
, constraint cust_actor_actor_fk foreign key (actor_id)
references actors (actor_id)
)
/
The TASKS table is rather unsurprising, given what's gone before:
create table tasks
(task_code varchar2(4) not null
, actor_id number not null
, constraint task_pk primary key (task_code, actor_id)
, constraint task_task_fk ask foreign key (task_code)
references task_types (task_code)
, constraint task_actor_fk foreign key (actor_id)
references actors (actor_id)
/
I agree all those intersection tables look like a lot of overhead but there isn't any other way to enforce foreign key constraints. The additional snag is creating ACTORS and CUSTOMER_ACTORS records every time you create a record in CUSTOMERS. Ditto for deletions. The only good news is that you can generate all the code you need.
Is this solution better than a table with one hundred optional foreign keys? Perhaps not: it's a matter of taste. But I like it better than having no foreign keys at all. If there is on euniversal truth in database practice it is this: databases which rely on application code to enforce relational integrity are databases riddled with children referencing the wrong parent or referencing no parent at all.
I have a MySQL table consisting of:
CREATE TABLE `url_list` (
`id` int(10) unsigned NOT NULL auto_increment,
`crc32` int(10) unsigned NOT NULL,
`url` varchar(512) NOT NULL,
PRIMARY KEY (`id`),
KEY `crc32` (`crc32`)
);
When inserting data into a related table I need to lookup the primary key from this table, and using the crc32 really speeds that up whilst allowing a small index. The URLs do need to be unique, but I'd like to avoid having more index than actual data.
If the value isn't present I need to insert it, but using structures such as INSERT IGNORE, or ON DUPLICATE KEY either requires me to put a unique on the huge varchar, or don't take advantage of my index.
How can I "SELECT id else INSERT", whilst preserving the lookup speed for the 80-90% of hits that are already in the table?
I would recommend ditching the id column and the crc32 because they're not necessary.
You can use an MD5() hash to provide a fixed-length, virtually unique value computed from the lengthy URL data, and then use that hash as the primary key.
CREATE TABLE `url_list` (
`url_hash` BINARY(16) NOT NULL PRIMARY KEY
`url` VARCHAR(512) NOT NULL
);
DELIM !!
CREATE TRIGGER `url_ins` BEFORE INSERT ON `url_list`
FOR EACH ROW
BEGIN
SET NEW.`url_hash` = UNHEX( MD5( NEW.`url` ) );
END!!
Then you can use INSERT..ON DUPLICATE KEY UPDATE because unlike crc32, the hash should have a very low chance of collision.
edit: See http://en.wikipedia.org/wiki/Birthday_attack. If you log 1 million distinct URL's per day for 2,000 years, the MD5 hashes of these URL's are still less likely to include a collision than your hard disk is to have an uncorrectable bit error.
This website offers a solution to a similar problem.