Below is the code snippet which I need to improve.
CREATE OR REPLACE T_CHANGE AFTER ---Trigger Created for After insert/update option
INSERT OR
UPDATE OF QTY ON ABC BEGIN
IF INSERTING THEN
UPDATE XYZ D SET FLAG_CHG = 1
WHERE EXISTS
(
SELECT 1 FROM XYZ D WHERE
:NEW.PRODUCT = D.PRODUCT AND
:NEW.LOCATION = D.LOCATION
);
IF UPDATING THEN
UPDATE XYZ D SET FLAG_CHG = 1
WHERE EXISTS
(
SELECT 1 FROM XYZ D WHERE
:OLD.PRODUCT = D.PRODUCT AND
:OLD.LOCATION = D.LOCATION `enter code here`
);
END IF
END T_CHANGE;
The two mentioned tables are as follow:
CREATE TABLE XYZ (
PRODUCT VARCHAR2(50),
LOCATION VArchar2(50),
FLAG_CHG BOOLEAN DEFAULT 0,
CONSTRAINT XYZ_PK PRIMARY KEY (PRODUCT,LOCATION)
)
CREATE TABLE ABC (
PRODUCT VARCHAR2(50),
LOCATION VArchar2(50),
QTY NUMBER,
CONSTRAINT ABC_PK PRIMARY KEY (PRODUCT,LOCATION)
)
What are you trying to achieve ?
1)If the QTY in ABC is updated or inserted the FLAG_CHG in XYZ should be updated to 1.
I have few queries on this
1.) Will the above code work? :P
2.) If works, will it have performance issues ?
3.) How can I enhance this code to improve the performance ?
4.) Please advice a better approach ,if any,to fulfill the requirement?
Thanks in Advance.
It won't work because SQL won't recognize what you are going to do there, I guess.
The better approch for it is to create some unique fields in your table, and then do query INSERT .... ON DUPLICATE KEY UPDATE ...
Reference
UPDATE on DUPLICATE KEY ORACLE
Related
Brief model overview:
I have a student and a course tables. As it's many to many relation there is also a junction table student_course (id_student, id_course), with unique constraint on both columns (composite).
The problem I want to solve:
On account of a mistake, there is no a unique constraint on the code column of the course table. It should as code column should uniquely identify a course. As a result there are two rows in the course table with the same value in the code column. I want to remove that duplicate, check that there is no other duplicates and add a unique constraint on the code column. Without loosing relations with student table.
My approach to solve the issue:
I have create a procedure that should do what I want.
CREATE OR REPLACE PROCEDURE REMOVE_COURSES
(
v_course_code IN VARCHAR2,
v_course_price IN VARCHAR2
)
AS
new_course_id NUMBER;
BEGIN
INSERT INTO course (CODE, PRICE) VALUES (v_course_code, v_course_price)
RETURNING ID INTO new_course_id;
FOR c_course_to_overwrite IN (SELECT *
FROM course
WHERE code = v_course_code AND id != new_course_id) LOOP
UPDATE student_course SET id_course = new_course_id WHERE id_course = c_course_to_overwrite.id;
DELETE FROM course WHERE id = c_course_to_overwrite.id;
END LOOP;
END REMOVE_COURSES;
/
Main problem I want to solve:
The procedure keeps giving me an error about unique constraint violation on student_course table. But I am really not sure how it's possible as I am using new_course_id, so there is no chance that in the junction table there are two rows with the same id_student, id_course. What do I need to fix ?
Miscellaneous:
I want to solve that issue using procedure only for learning purposes
EDITED:
CREATE TABLE student (
id NUMBER GENERATED BY DEFAULT ON NULL AS IDENTITY,
name VARCHAR2(150) NOT NULL,
PRIMARY KEY (id)
);
ALTER TABLE student MODIFY ID
GENERATED BY DEFAULT ON NULL AS IDENTITY (START WITH LIMIT VALUE);
CREATE TABLE course (
id NUMBER GENERATED BY DEFAULT ON NULL AS IDENTITY,
code VARCHAR2(255) NOT NULL,
PRIMARY KEY (id)
);
ALTER TABLE course MODIFY ID
GENERATED BY DEFAULT ON NULL AS IDENTITY (START WITH LIMIT VALUE);
CREATE TABLE student_course (
id_student NUMBER NOT NULL,
id_course NUMBER NOT NULL,
PRIMARY KEY (id_student, id_course),
CONSTRAINT student_fk FOREIGN KEY (id_student) REFERENCES student (id),
CONSTRAINT course_fk FOREIGN KEY (id_course) REFERENCES course (id)
);
insert into student (name) values ('John');
INSERT INTO course (ID, CODE) VALUES (1, 'C_13');
INSERT INTO course (ID, CODE) VALUES (2, 'C_13');
commit;
INSERT INTO STUDENT_COURSE (ID_STUDENT, ID_COURSE) VALUES (1, 1);
INSERT INTO STUDENT_COURSE (ID_STUDENT, ID_COURSE) VALUES (1, 2);
commit;
CALL REMOVE_COURSES('C_13');
[23000][1] ORA-00001: unique constraint (SYS_C0014983) violated ORA-06512: near "REMOVE_COURSES", line 8
Rather than removing one of the duplicate codes, you're creating a third course with the same code, and trying to move all students on either of the old courses onto the new one. The error suggests you have students who are already enrolled on both of the old courses.
Your cursor loop query is:
SELECT *
FROM course
WHERE code = v_course_code AND id != new_course_id
That will find all junction records for both old versions of the code, and the update then sets all of those junction records to the same new ID.
If there are any students listed against both old IDs for the code - which would be allowed by your composite unique key - then they will both be updated to the same new ID.
So say the courses you're looking at are [updated for your example code]:
ID CODE
-- ----
1 C_13
2 C_13
and you have junction records for a student for both courses, like:
ID_STUDENT ID_COURSE
---------- ---------
1 1
1 2
You are creating a new course:
ID CODE
-- ----
3 C_13
Your cursor loop looks for code = 'ABC' and ID != 3, which finds IDs 1 and 2. So in the first iteration of the loop up update the rows with ID 1, so now you have:
ID_STUDENT ID_COURSE
---------- ---------
1 3
1 2
Then in the second iteration you try to update the rows with ID 2, which would attempt to produce:
ID_STUDENT ID_COURSE
---------- ---------
1 3
1 3
which would break the unique constraint - hence the error.
You probably don't want to create a new course at all, but either way, you need to remove duplicate records from student_course - that is, rows which will become duplicates when updated. Basically you need to find students with entries for both existing course IDs, and delete either of them. If you don't care which this would do it:
delete from student_course sc1
where id_course in (
select id
from course
where code = 'C_13'
)
and exists (
select null
from student_course sc2
join course c on c.id = sc.id_course
where sc2.id_student = sc1.id_student
and sc2.id_course > sc1.id_course
and c.code = 'C_13'
);
but there are other (probably better) ways.
You then have the choice of updating all remaining junction records for both old IDs to your new ID; or to consolidate on one of the old IDs and remove the other.
(Your question implies you want to solve the overall task yourself, so I'll refrain from trying to provide a complete solution - this just hopefully helps you understand and resolve your main problem...)
I have a problem like
Table A:
-- TableBCId
Table B:
-- Id
Table C:
-- Id
I am looking for a way to create a foreign key table A where an entry can be either in table B or table C
Example entries:
Table A:
-- TableBCId: 1
-- TableBCId: 2
Table B:
-- Id: 1
Table C:
-- Id: 2
I want to avoid if possible:
- Two columns in table A
- Default values
- Additional tables
- Creation of an base entity is not possible
Every idea welcome
The normal way to implement this requirement is with 2 columns, 2 foreign key constraints, and a check constraint to ensure exactly of of the columns populated (if this is a requirement):
create table a
( ...
, b_id references b
, c_id references c
, constraint <name> check ( (b_id is null and c_id is not null)
or (b_id is not null and c_id is null)
)
);
You could, if it helps your UI, create a view over that table that combines B_ID and C_ID into a single column.
But you have said you don't want 2 columns, why is that?
The reason why this is hard is because the data model is wrong. A foreign key references only one table. A table can have more than one foreign key but each is separate. Apart from anything else, how would you know whether bc_id referenced b.id or c.id?
One explanation for this scenario is that table A should really be two tables, BA referencing B and CA referencing C. Alternatively A should reference a super-type table, of which B and C are sub-types. Without knowing the actual business domain it's hard to be sure.
Anyway, the path of least change is two columns.
You can use a insert/update trigger on your Table_A.
Maybe something like this:
CREATE TRIGGER Table_a_trgr
BEFORE INSERT OR UPDATE
on Table_a
FOR EACH ROW
DECLARE
c_row NUMBER;
BEGIN
SELECT count(*)
INTO c_row
FROM (
SELECT ID FROM table_b WHERE id = :NEW.TableBCId
UNION ALL
SELECT ID FROM table_c WHERE İd = :NEW.TableBCId
)
;
IF c_row < 2 THEN
raise_application_error(-20000, 'Error, Foreign Key');
END IF;
END;
/
If you don't want to make a new column in table A.
Then you can make a parent table to B and C.
tableBC:
id
And then create a 1-1 relation with tables B and C to table BC.
tableB:
id,
parent -- 1-1 foreign key to tableBC
tableC:
id,
parent -- 1-1 foreign key to tableBC
Now, in table A
tableA:
id,
TableBCId -- foreign key to tableBC
We have solved a similar problem using this approach.
Is there anyway that we can set a constraint in database table level to have upper or lower case values for certain columns? When we create a table, we can set NOT NULL to avoid having null values on a column. Same way, can we do that for either uppercase or lower case?
You can do that using a check constraint:
create table foo
(
only_lower varchar(20) not null check (lower(only_lower) = only_lower),
only_upper varchar(20) not null check (upper(only_upper) = only_upper)
);
I had almost same case, tried with check constraint, but if the user is not mentioning it as UPPER() or LOWER() it gives error so I took TRIGGER route as below code.
--creating table
create table user_name (
first_name varchar2(50),
last_name varchar2(50));
--creating trigger
CREATE OR REPLACE TRIGGER TRG_USER_NAME_IU
BEFORE INSERT OR UPDATE ON USER_NAME
FOR EACH ROW
BEGIN
:NEW.FIRST_NAME := UPPER(:NEW.FIRST_NAME);
:NEW.LAST_NAME := UPPER(:NEW.LAST_NAME);
END;
/
Can test and share feedback or comments
I have an oracle database and one of the tables contains monetary fields:
desc example_table;
Name Null Type
--------- -------- ------
...
PRICE NOT NULL NUMBER
SHIPPING NUMBER
DISCOUNT NUMBER
...
I need to modify this table to also contain corresponding currency codes for each of the fields. And these new columns need to be populated with default values corresponding to the columns that already exist.
Here is my thought on how to do this:
alter table example_table add (
price_currency_code varchar2(3)
, shipping_currency_code varchar2(3)
, discount_currency_code varchar2(3)
);
update example_table
set price_currency_code = 'USD'
, shipping_currency_code = case when shipping is null
then null
else 'USD'
end
, discount_currency_code = case when discount is null
then null
else 'USD'
end
;
Lastly, I need to make sure that the nullable property of each new column matches that of the original columns:
alter table example_table modify (
price_currency_code varchar2(3) not null
);
Is this the correct (and best performance) solution to solve this problem? Is there another way to accomplish the same results that might perform better on a table that contains hundreds of millions of rows?
If this approach is used to update a production table for a website, how might this update affect the user experience on the website while the update is running?
You can use the trick that Justin mentioned, e.g.:
alter table example_table add (
price_currency_code varchar2(3) default 'USD' not null
, shipping_currency_code varchar2(3)
, discount_currency_code varchar2(3)
);
alter table example_table modify price_currency_code default null;
This allows you to set all the existing rows to 'USD' but not have the default remain for subsequent inserts. Of course, if 'USD' is a sensible default then you could skip the second alter.
Then, it's just a matter of the other columns. Depending on the number of rows that meet the conditions, you may choose to have one update statement or two, e.g.:
update example_table set shipping_currency_code = 'USD' where shipping is not null;
update example_table set discount_currency_code = 'USD' where discount is not null;
If there are a large number of records involved you may need a different strategy.
Another option to consider is to use DBMS_REDEFINITION.
I've created the following two object types :
create or replace type person_typ as object (
person# varchar(10)
) not final;
create or replace type salesperson_typ under person_typ (
salesperson# varchar(10),
sSurname varchar(10),
sForename varchar(10),
dateOfBirth date
);
create table person_tab of person_typ (
person# primary key
);
And I've inserted a row using :
insert into person_tab
values (salesperson_typ('p1','s1', 'Jones', 'John', sysdate));
Which I can retrieve using the following :
select
treat(value(s) as salesperson_typ).person# as person_number,
treat(value(s) as salesperson_typ).sSurname as sSurname
from
person_tab s
;
However, if I look at person_tab I only see the following :
SQL> select * from person_tab;
PERSON#
----------
p1
I'm curious, where does the salesperson specific data get stored? I was almost expecting to find a salesperson table, but I can't find anything obvious.
Your object is stored invisibly in the same table.
You can check columns by querying USER_TAB_COLS:
SELECT *
FROM user_tab_cols
WHERE table_name = 'PERSON_TAB';
Then you can then use the column names* you just discovered in a query (except SYS_NC_ROWINFO$, that throws an error for me).
SELECT SYS_NC_OID$
,SYS_NC_TYPEID$
--,SYS_NC_ROWINFO$
,PERSON#
,SYS_NC00005$
,SYS_NC00006$
,SYS_NC00007$
,SYS_NC00008$
FROM PERSON_TAB;
Note*
You should not use these column names in any application because they are internal and subject to change in future patches/releases.