I have two tables in my system EMPLOYEE and EMPLOYEE_FORECAST. Both have the same columns, entire structure is same. I have another archive table with same structure called EMPLOYEE_ARCHIVE table.
I need to put data from both tables to this archive table. Since records in EMPLOYEE and EMPLOYEE_FORECAST may have same primary key e.g. a record in EMPLOYEE will have a pk of say 100 and another record in EMPLOYEE_FORECAST may also have pk of 100 and this will definitely happen so when they are inserted into archive table I will have a duplicate primary key.
The problem is I will also have some relation table like employee_products, employee_forecast_products and also employee_archive_products. These tables will have emp_id and product_id. So with same emp_id I wont be able to figure out the exact employee.
So, is there any way to have a unique primary key both the EMPLOYEE and EMPLOYEE_FORECAST tables.
So you cannot not use the PK column of EMPLOYEE table as a PK column of the archive table.
You can add a new PK column to the archive table.
If, for some reason, you want the EMPLOYEE table's PK column to be the PK in the archive table, then you could add a flag column to the archive table which would indicate from which table the record comes from. And you could have a composite PK in the archive table containing the original PK and the flag column. (In general, I discourage composite PK-s, so, even if you want to have this flag column, you could have an additional normal PK column in the archive as well.)
To expand on my comment, set up you archive table as:
EMPLOYEE
EMPID NUMBER PK
EMPNAME VARCHAR2(30)
...
EMPLOYEE_FORECAST
EMPID NUMBER PK
EMPNAME VARCHAR2(30)
...
EMPLOYEE_ARCHIVE
ORIG_TABLE VARCHAR2(30) PK
EMPID NUMBER PK
EMPNAME VARCHAR2(30)
...
Data in EMPLOYEE_ARCHIVE:
ORIG_TABLE EMPID EMPNAME
------------------------------------
EMPLOYEE 100 JO BLOGGS
EMPLOYEE_FORECAST 100 JO BLOGGS
As the archive table PK is across both the original table and empid columns it will remain unique for all your data.
Obviously this is just an example and you can use whatever derived column you want to enforce the uniqueness in your archive table.
Hope it helps...
Create a Common Super-Table. Make another table EMPLOYEE_ID with only a primary key. Let both EMPLOYEE, EMPLOYEE_FORECAST and EMPLOYEE_ARCHIVE reference it.
Your data model seems a tad confused. If EMPLOYEE and EMPLOYEE_FORECAST have identical structures why have two tables? What is the business rule here?
And if they are supposed to be two separate tables why store them in a common archive table? Why not have separate archives for each table?
I agree with #Ollie. You need to rethink your data model so it clearly expresses how your business operates. If you post your business rules here I'm sure we can help you untangle things. But here is probably the crucial question: do the following keys identify one employee (i.e one person in the real world) or two?
employee.emp_id = 100
employee_forecast.emp_id = 100
Related
I am new to Hive and have some problems. I try to find a answer here and other sites but with no luck... I also tried many different querys that come to my mind, also without success.
I have my source table and i want to create new table like this.
Were:
id would be number of distinct counties as auto increment numbers and primary key
counties as distinct names of counties (from source table)
You could follow this approach.
A CTAS(Create Table As Select)
with your example this CTAS could work
CREATE TABLE t_county
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE AS
WITH t AS(
SELECT DISTINCT county, ROW_NUMBER() OVER() AS id
FROM counties)
SELECT id, county
FROM t;
You cannot have primary key or foreign keys on Hive as you have primary key on RBDMSs like Oracle or MySql because Hive is schema on read instead of schema on write like Oracle so you cannot implement constraints of any kind on Hive.
I can not give you the exact answer because of it suppose to you must try to do it by yourself and then if you have a problem or a doubt come here and tell us. But, what i can tell you is that you can use the insertstatement to create a new table using data from another table, I.E:
create table CARS (name string);
insert table CARS select x, y from TABLE_2;
You can also use the overwrite statement if you desire to delete all the existing data that you have inside that table (CARS).
So, the operation will be
CREATE TABLE ==> INSERT OPERATION (OVERWRITE?) + QUERY OPERATION
Hive is not an RDBMS database, so there is no concept of primary key or foreign key.
But you can add auto increment column in Hive. Please try as:
Create table new_table as
select reflect("java.util.UUID", "randomUUID") id, countries from my_source_table;
I'm looking through our data and there's a handful of tables in our oracle database that show up with two one to many relationships: http://i.stack.imgur.com/icGcV.png
I'm not sure why this would be happening, and is it something I should look into getting changed or fixed?
(I did not create this database, I am only trying to understand it!)
Too long for a comment, let's see a very simple example:
CREATE TABLE persons
(
id NUMBER PRIMARY KEY,
name VARCHAR2(10)
)
/
CREATE TABLE marriages
(
wife NUMBER REFERENCES persons(id),
husband NUMBER REFERENCES persons(id)
)
/
CREATE TABLE dogs
(
id NUMBER PRIMARY KEY,
name VARCHAR2(10),
owner NUMBER REFERENCES persons(id)
)
/
Here you have one table with two different FKs to the same table. At the same time you have another table with a single FK to the same table.
So, it's not a problem to fix, but a part of DB design to understand;
your DB can be well or bad designed, but the existence of such situations does not say anything about that.
I have one table with a composite key (REGION) and another table (CITY) that references that table. Inserts, queries, and individual deletions work quickly. The problem is that when I try to bulk-delete the contents of CITY using sqlplus, delete from CITY, it takes forever. This table will have ~400,000 entries and it takes 15-20 minutes just to delete 50,000 entries. Here is my setup using Oracle 11:
create table COUNTRY
(
id varchar2(32) NOT NULL -- PK
...
);
create table REGION -- about 4000 entries
(
country varchar2(32) NOT NULL -- PK, FK to COUNTRY
regionCode char(2) NOT NULL -- PK
...
);
create table CITY -- about 400,000 entries
(
id number NOT NULL -- PK
country varchar2(32) NOT NULL -- FK to COUNTRY
regionCountry varchar2(32) NULL -- FK to REGION
regionCode char(2) NULL -- FK to REGION
...
);
create table LOCATION -- about 2,500,000 entries
(
id varchar2(32) NOT NULL -- PK
country varchar2(32) NOT NULL -- FK to COUNTRY
city number NULL -- FK to CITY
...
);
ALTER TABLE COUNTRY ADD CONSTRAINT PK_COUNTRY PRIMARY KEY (id) USING INDEX;
ALTER TABLE REGION ADD CONSTRAINT PK_REGION PRIMARY KEY (country, regionCode) USING INDEX;
ALTER TABLE CITY ADD CONSTRAINT PK_CITY PRIMARY KEY (id) USING INDEX;
ALTER TABLE IPGeoLoc ADD CONSTRAINT PK_LOCATION PRIMARY KEY (id) USING INDEX;
ALTER TABLE REGION ADD CONSTRAINT FK_REGION_COUNTRY
FOREIGN KEY (country) REFERENCES COUNTRY (id);
ALTER TABLE CITY ADD CONSTRAINT FK_CITY_COUNTRY
FOREIGN KEY (country) REFERENCES COUNTRY (id);
ALTER TABLE CITY ADD CONSTRAINT FK_CITY_REGION
FOREIGN KEY (regionCountry, regionCode) REFERENCES REGION (country, regionCode);
ALTER TABLE LOCATION ADD CONSTRAINT FK_LOCATION_COUNTRY
FOREIGN KEY (country) REFERENCES COUNTRY (id);
ALTER TABLE LOCATION ADD CONSTRAINT FK_LOCATION_CITY
FOREIGN KEY (city) REFERENCES CITY (id);
The varchar2(32) fields are GUIDs. I know I should not use GUIDs as a PK but I cannot change that unless I have proof that this is the problem.
I can bulk-delete entries from LOCATION with no problem, 300,000 in a couple of seconds, so this leads me to believe it is the composite key that is giving me trouble.
The secondary issue is that I currently have two country columns in the CITY table - one linked directly to COUNTRY and the other linked as part of the composite key to REGION. I know how I would do this in code and only have one country column but I have to use Hibernate. This works the way it is except for the delete problem so I can't change it unless I can prove this is causing an issue. I'm using sqlplus to try the deletions so I know Hibernate is not causing the delete problem.
My wager is that the problem has nothing to do with the presence of a composite key and everything to do with an unindexed foreign key.
Unless you've omitted it from your question, the CITY column in the LOCATION table is not indexed. That means that every time you try to delete a row from CITY, Oracle has to do a full table scan on the LOCATION table looking for rows in LOCATION that would be orphaned in order to enforce the foreign key constraint. In general, if you want to ever delete from the parent, the foreign key in the child table needs to be indexed. So LOCATION should have indexes on both CITY and COUNTRY, the CITY table should have indexes on COUNTRY and (regionCountry, regionCode), etc.
Even if all the rows from LOCATION have been deleted, if Oracle has to do a full table scan on LOCATION, it has to read up to the high water mark of the table. If the table previously had 2.5 million rows and you just did a DELETE, you would still have to read however many blocks were required to store those 2.5 million rows every time you delete a row from CITY.
You can test whether my hunch is correct in a few different ways
You can index the CITY column in the LOCATION table.
You can drop the foreign key constraint on LOCATION that references the CITY table.
You can truncate the LOCATION table instead of deleting the rows so that the high water mark gets reset and a table scan will take much less time.
Say there are two tables, Company and Employee. Employee has a foreign key to Company and Company has a foreign key to Employee. How should I insert and delete data into these tables without getting referential integrity errors?
COMPANIES
ID
NAME
CONTACT_EMPLOYEE_ID --FK
EMPLOYEES
ID
NAME
COMPANY_ID --FK
I imagine this is a fairly common problem. I have researched it but have been unable to find much information. Perhaps the problem comes under a more common name I am not aware of.
There are several methods available:
Is the CONTACT_EMPLOYEE_ID column nullable? If it is, just insert company, insert employee and then update the company record.
You could also set one of the constraints as deferrable. You could then set the constraint as deferred, insert both records and then commit.
There are generally 2 strategies:
Leave one of the FKs NULL-able (and then insert NULL into that table, insert row into other table and finally update the NULL).
Defer one of the FKs.
You could even leave both FKs NULL-able or deferrable (or even a combination of the two), so you can perform the insertion in both directions.
You could also consider placing all the EMPLOYEES fields into COMPANIES.
Apart from the other suggestions already made, which are good (make one of the FK columns NULLable, or make the FK constraint deferrable), another one is to make the NOT NULL constraint deferrable, e.g.:
create table COMPANIES (
ID number not null,
NAME varchar2(100) not null,
CONTACT_EMPLOYEE_ID number,
constraint contact_not_null
check (CONTACT_EMPLOYEE_ID not null)
deferrable
initially deferred
);
Now, you can insert a row with NULL for the employee id, insert the employee, then update companies.contact_employee_id with the new employee ID, then COMMIT.
I have this table in an Oracle DB which has a primary key defined on 3 of the data columns. I want to drop the primary key constraint to allow rows with duplicate data for those columns, and create a new column, 'id', to contain an auto-incrementing integer ID for these rows. I know how to create a sequence and trigger to add an auto-incrementing ID for new rows added to the table, but is it possible to write a PL/SQL statement to add unique IDs to all the rows that are already in the table?
Once you have created the sequence:
update mytable
set id = mysequence.nextval;
If you're just using an integer for a sequence you could update the id with the rownum. e.g.
update
table
set id = rownum
You then need to reset the sequence to the next valid id.
Is this what you need?
UPDATE your_table
SET id = your_seq.nextval;
This assumes you don't care what order your primary keys are in.
First you should check your PCTFREE... is there enough room for every row to get longer?
If you chose a very small PCTFREE or your data has lots of lenght-increasing updates, you might begin chaining every row to do this as an update.
You almost certainly better to do this as a CTAS.
Create table t2 as select seq.nextval, t1.* from t1.
drop t1
rename t2 to t1.