I have 2 tables in PostgreSQL
Table A : https://2.pik.vn/201819cbcc97-8d59-4d3f-9e47-38b5e33d00df.jpg
Table B : https://2.pik.vn/20186c925ba2-7c9c-4253-ba28-497df1465b4f.jpg
I want to create a trigger in PostgeSQL so if I update value in column area in table A, the value in area_LUA will automatically change in table B.
area_LUA = total sum (area)*100 with condition A.parent_id = B.parent_id and CODE ='LUA'
Can someone guide me how to create a trigger like this? Thank you so much
The following trigger should get the job done.
Trigger area_lua will execute after each update on table A. Trigger function update_area_lua checks if the value of area changed, and accordingly updates column area_LUA in table B, with respect to the given parent_id.
CREATE OR REPLACE FUNCTION update_area_lua()
RETURNS trigger AS
$BODY$
BEGIN
IF NEW.area <> OLD.area THEN
UPDATE B
SET area_LUA = (
SELECT SUM(area) * 100
FROM A
WHERE parent_id = B.parent_id AND CODE ='LUA'
)
WHERE parent_id = NEW.parent_id;
END IF;
RETURN NEW;
END;
$BODY$
CREATE TRIGGER area_lua
AFTER UPDATE
ON A
FOR EACH ROW
EXECUTE PROCEDURE update_area_lua();
Related
I have subscription data that is being appended to a table in real-time (via kafka). i have set up a trigger such that once the data is added it is checked for consistency. If checks pass some of the data should be added to other tables (that have master information on the customer profile etc.). The checks function i wrote works fine but i keep getting errors on the function used in the trigger. The function for the trigger is:
CREATE OR REPLACE FUNCTION update_tables()
RETURNS TRIGGER
LANGUAGE plpgsql
AS
$$
BEGIN
CASE (SELECT check_incoming_data()) WHEN 0
THEN INSERT INTO
sub_master(sub_id, sub_date, customer_id, product_id)
VALUES(
(SELECT sub_id::int FROM sub_realtime WHERE CTID = (SELECT MAX(CTID) FROM sub_realtime)),
(SELECT sub_date::date FROM sub_realtime WHERE CTID = (SELECT MAX(CTID) FROM sub_realtime)),
(SELECT customer_id::int FROM sub_realtime WHERE CTID = (SELECT MAX(CTID) FROM sub_realtime)),
(SELECT product_id::int FROM sub_realtime WHERE CTID = (SELECT MAX(CTID) FROM sub_realtime))
);
RETURN sub_master;
END CASE;
RETURN sub_master;
END;
$$
The trigger is then:
CREATE TRIGGER incoming_data
AFTER INSERT
ON claims_realtime_3
FOR EACH ROW
EXECUTE PROCEDURE update_tables();
What I am saying is 'if checks pass then select data from the last added row and add them to the master table'. What is the best way to structure this query?
Thanks a lot!
The trigger functions are executed for each row and you must use a record type variable called "NEW" which is automatically created by the database in the trigger functions. "NEW" gets only inserted records. For example, I want to insert data to users_log table when inserting records to users table.
CREATE OR REPLACE FUNCTION users_insert()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
begin
insert into users_log
(
username,
first_name,
last_name
)
select
new.username,
new.first_name,
new.last_name;
return new;
END;
$function$;
create trigger store_data_to_history_insert
before insert
on users for each row execute function users_insert();
I want to create a trigger which checks before insert if the tupel which is supposed to be inserted holds a specific condition (which also depends on another table).
For example:
create trigger or replace check_tupel
before insert on A
for each row
execute
if exists (select x,y from B where B.x = A.x and B.y = A.y)
Oh I am using postgreSQL 13.
EDIT: Yes I know that I can do this without a trigger, but I am asking for a solution with a trigger for a reason.
I hope there is a way to do this... My other idea was to create a UDF which gets called before insert but I do not know how to check the condition in this UDF and only insert if the function returns true.
If you simply wanna automatically validate a record before inserting it on table A based on table B using a User Defined Function, you do not need a trigger at all. Consider adding a simple CHECK CONSTRAINT:
CREATE TABLE a (
x int,
y int,
CONSTRAINT exists_in_b CHECK (NOT myfunc(x,y))
);
Demo: db<>fiddle
CREATE TABLE b (x int,
y int);
INSERT INTO b VALUES (42,42);
CREATE OR REPLACE FUNCTION myfunc(x int, y int)
RETURNS BOOLEAN AS $BODY$
SELECT EXISTS (SELECT 1 FROM b WHERE b.y =$1 AND b.x=$2 )
$BODY$
LANGUAGE sql;
CREATE TABLE a (
x int,
y int,
CONSTRAINT exists_in_b CHECK (NOT myfunc(x,y)) -- here the magic happens
);
Now, if we try to insert a value that our function does not validate, it raises an exception:
INSERT INTO a VALUES (42,42);
ERROR: new row for relation "a" violates check constraint "exists_in_b"
DETAIL: Failing row contains (42, 42).
SQL state: 23514
EDIT (See comments): Solution using a trigger
CREATE OR REPLACE FUNCTION myfunc()
RETURNS TRIGGER AS $BODY$
BEGIN
IF EXISTS (SELECT 1 FROM b WHERE b.y =NEW.y AND b.x=NEW.x ) THEN
RAISE EXCEPTION 'tuple already exists in "b": % %', NEW.x,NEW.y;
END IF;
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql;
CREATE TRIGGER check_tupel
BEFORE INSERT OR UPDATE ON a
FOR EACH ROW EXECUTE PROCEDURE myfunc();
Demo: db<>fiddle
So you need a trigger solution, sounds like a homework problem. The question then becomes do you want to:
abort the entire operation
slightly squash the row but continue the remainder of the operation.
The following does the second: (See demo)
create or replace
function check_b_has_a()
returns trigger
language plpgsql
as $$
begin
if exists
( select null
from b
where (b.x,b.y) =
(new.x, new.y)
)
then
return null;
else
return new;
end if;
end;
$$;
create trigger a_bir
before insert
on a
for each row
execute function check_b_has_a();
I have two tables as follows:
Table A: Name, ID, value
Table B: ID, title
TableA.value is dependent on whether TableA.ID is present in TableB.ID.
I am trying to create a procedure and trigger so that whenever TableB is modified, the procedure is triggered to check if TableA.ID is in TableB.ID and sets TableA.value to 10.
I am using the following code and getting an error:
CREATE PROCEDURE update1
LANGUAGE SQL
AS $$
UPDATE tablA as a
SET a.value = 10
WHERE a.ID EXISTS ( SELECT b.ID
FROM tableB as b
WHERE a.ID = b.ID)
$$;
I am an SQL noob, and this is the first time I am trying to use a procedure.
UPDATE
I was able to create a procedure which does the job when I manually run it using CALL
However, it does not have a RETURNS TRIGGER block within it. Adding that returns the error Procedure cannot return triggers.
If I create a trigger as follows
CREATE TRIGGER b_trigger
AFTER UPDATE OR INSERT ON b.ID
FOR EACH STATEMENT
EXECUTE PROCEDURE update1();
However, this returns the following
ERROR: function columbia_deli.manager_discount must return type trigger
SQL state: 42P17
Try this using plpgsql Language:
Trigger Function:
CREATE OR REPLACE FUNCTION update1()
RETURNS trigger AS
$BODY$
begin
update "TableA" set value= 10 where id =new.id;
return NEW;
end;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
Then create trigger on TableB for after update event
CREATE TRIGGER trig_tableb
AFTER UPDATE
ON "TableB"
FOR EACH ROW
EXECUTE PROCEDURE update1();
I'm new to SQL and I'm trying to update a column (ex_counter) of a table (ex_table). This column consists of a counter of the number of times an ID (ex_id) appears on a second table (ex2_id in ex2_table).
An ID can be inserted into the second table at any moment. If that ID is already existing, the counter of its corresponding ID in the first table must be updated (by simply adding 1, I guess).
These are the two tables:
CREATE TABLE ex_table(
ex_id SMALLINT,
ex_counter SMALLINT;)
CREATE TABLE ex2_table(
ex2_id SMALLINT;)
I think it should be done more or less like this. The commented code is the pseudocode that I don't know how to implement:
CREATE TRIGGER ex_trigger AFTER
INSERT ON ex2_table
FOR EACH ROW EXECUTE PROCEDURE ex_func();
CREATE FUNCTION ex_func() RETURNS trigger AS $$ BEGIN
/*
if ex2_id = ex_id
ex_counter = ex_counter + 1
*/
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
Thanks in advance!
Something like this
IF EXISTS (SELECT * FROM ex_table WHERE ex_id = new.ex2_id) THEN
UPDATE ex_table
SET ex_counter = ex_counter + 1
WHERE ex_id = new.ex2_id
ELSE
INSERT INTO ex_table VALUES (new.ex2_id, 1)
END IF;
Note that it is no point really to store a counter since you so easily can retrieve the value by doing a SELECT COUNT()...
I came from Microsoft SQL environment.I have two tables tak_ne and tak_beb and my requirement was to insert values from tak_beb to tak_ne if value is not present,if it is present just update.So i made a merge statement as shown below.But the problem now i am facing is veryday 50000 count is getting increment for sequence number.Oracle is stable database, and i don't know why they made it like that.So i create a Function and prevented incrementing sequence number.My question is ,is it a right approach by creating function.Following is what i did
merge into tak_ne a using tak_beb b ON (a.NAME=b.NAME)
When matched then
Update
Set a.AC_NO = b.AC_NO
a.LOCATION = b.LOCATION
a.MODEL = b.MODEL
When not matched then
insert
(
sl_no,
AC_NO,
LOCATION
MODEL
)
Values
(
s_slno_nextval
b.AC_NO
b.LOCATION
b.MODEL
)
and then i created a function
CREATE OR REPLACE FUNCTION s_slno_nextval
RETURN NUMBER
AS
v_nextval NUMBER;
BEGIN
SELECT s_emp.nextval
INTO v_nextval
FROM dual;
RETURN v_nextval;
END;
Oracle uses this approach to generate unique id for each row inserted by a statement. Your TAK_BEB table has probably 50000 rows, so the sequence is incremented 50000 times.
To hide increment into a function does not help. Function is called AND EXECUTED for every row, it increments sequence for 50000 times again. And it adds overhead with 50000 selects from dual table.
If you really need to use ONE value from sequence for ALL rows inserted by statement, use package variable:
create package single_id_pkg is
id Number;
function get_id return number;
end;
/
create or replace package body single_id_pkg is
function get_id return number is
begin
return id;
end;
end;
/
Now use for example before statement trigger on table to set the variable:
create trigger tak_ne_BSI_trg
before insert
on tak_ne
begin
select s_emp.nextval
into single_id_pkg.id
from dual;
end;
Insert trigger has one disadvantage - with MERGE clause it fires even if the statement does only updates rows (see https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:25733900083512). If it is a problem, you have to initialize the variable in other way.
Next modify your statement to use a package variable:
merge into tak_ne a
using tak_beb b
on (a.NAME=b.NAME)
when matched then
update
set a.AC_NO = b.AC_NO
a.LOCATION = b.LOCATION
a.MODEL = b.MODEL
when not matched then
insert (sl_no,
AC_NO,
LOCATION,
MODEL)
values (single_id_pkg.get_id
b.AC_NO,
b.LOCATION,
b.MODEL)
In Oracle standard way to use autoincrement field is by using sequences. And of course it will increment sequence number each time you want to use it.
But you can omit calling sequence_name.nextval, hiding it in trigger it is considered the standard approach also.
CREATE OR REPLACE EDITIONABLE TRIGGER TAK_NE_ID_TR"
BEFORE INSERT ON tak_ne
FOR EACH ROW
BEGIN
IF :old.sl_no IS NULL THEN
:new.sl_no := s_emp.nextval;
END IF;
END;
If you want to add same id for a batch of your inserts you can use global temporary table for saving it. For example, like this:
create global temporary table tak_ne_id ("id" number) on commit delete rows
create or replace trigger tak_ne_BSI_trg
before insert
on tak_ne
begin
insert into tak_ne_id("id")
values(s_emp.nextval);
end
create or replace TRIGGER TAK_NE_ID_TR
BEFORE INSERT ON tak_ne
FOR EACH ROW
BEGIN
if :old.sl_no is null then
SELECT "id"
INTO :new.sl_no
FROM tak_ne_id;
end if;
END;
Then you can use you merge as before, and without calling nextval:
merge into tak_ne a using tak_beb b ON (a.NAME=b.NAME)
When matched then
update
set a.AC_NO = b.AC_NO,
a.LOCATION = b.LOCATION,
a.MODEL = b.MODEL
When not matched then
insert
(
AC_NO,
LOCATION,
MODEL
)
Values
(
b.AC_NO,
b.LOCATION,
b.MODEL
);