I have an SQL file that contains the schema of the database (creating of tables and some functions to check the constraints). One of the functions has different actions to do for the first entered value and for the rest. What I mean is, that in the function I am firstly counting the number of elements in a table:
CREATE TABLE table_name(
column1 INT,
column2 INT CHECK(func())
);
CREATE OR REPLACE FUNCTION func1()
returns BOOLEAN
LANGUAGE plpgsql
AS
$$
BEGIN
SELECT COUNT(*) INTO var1 FROM table_name;
RAISE NOTICE 'count: %', var1;
IF var1 = 0 THEN
...
return true;
ELSE
...
return true;
END IF;
return false;
END;
$$;
...
and if it is 0, then it does some checks for the first element, and else it does a bit different checks. Then to insert the data I am using COPY(in another SQL file):
COPY table_name(column1, column2) FROM stdin;
5 2
8 7
\.
but I am getting an error:
ERROR: new row for relation "table_name" violates check constraint "table_name_check"
for the second row. So, I have added RAISE NOTICE to print the count in my schema(as shown in the first block of code above):
RAISE NOTICE 'count: %', var1;
and for the first insert, it gives me count = 0, but for the second I also get count = 0. That is why the function treats the second insert as if it is first and it causes errors. What could be the reason for this problem? It looks like even if the first row has been inserted, there are still no rows on the table after the first insertion.
Related
I need to add a trigger that raises a warning message when a certain out of bounds (not 2, 3, 5-7) numeric value is inserted into or altered in an EXISTING row in a "grade" column in the sql table. This code example raises such a message ONLY when a NEW row is created.
How to raise the message when a value in the EXISTING row is altered?
Values in the "grade" column are tied via key to a column in another table "grade_salary" where they are stored. How to write the insertion/alteration check in such a way that raises the message without specifying the concrete correct values (2, 3, 5-7), but stating only that "IF changed value lies outside of the values specified in column "grade" of the table "grade_salary" THEN raise the error message" (and not let the value be modified)?
CREATE TRIGGER person
BEFORE INSERT ON hr."position"
FOR EACH ROW EXECUTE PROCEDURE person();
CREATE OR REPLACE FUNCTION person()
RETURNS TRIGGER
SET SCHEMA 'hr'
LANGUAGE plpgsql
AS $$
BEGIN
IF ((NEW.grade < 2) or (NEW.grade > 3 and NEW.grade < 5)
or (NEW.grade > 7)) THEÎ
RAISE EXCEPTION 'Incorrect value';
END IF;
RETURN NEW;
END;
$$;
One checks whether the new value corresponds to an existing one in a column with:
IF new_value not in (SELECT DISTINCT grade FROM grade_salary)
THEN RAISE EXCEPTION 'Inadmissible value.'
In full:
CREATE OR REPLACE FUNCTION person()
RETURNS TRIGGER
SET SCHEMA 'hr'
LANGUAGE plpgsql
AS $$
declare
new_value numeric;
begin
select new.grade from "position" into new_value;
IF new_value not in (SELECT DISTINCT grade FROM grade_salary)
THEN RAISE EXCEPTION 'Inadmissible value.';
END IF;
RETURN NEW;
END;
$$;
I discovered a mysterious table named num in my database which has one column named count. I had no idea how it got there, then I realized it might be caused by a misbehaving trigger.
I have a trigger function:
DECLARE num integer := 0;
BEGIN
IF ... THEN
SELECT COUNT(*) INTO num FROM ...
END IF;
IF num > 1 THEN
DELETE FROM ...
END IF;
RETURN NEW;
END;
As you can see my purpose is to count the rows returned by a query and perform some operation if it is greater than one.
Can this faulty code be responsible for the unwanted table created? If so, how to fix this?
SELECT ... INTO foo in PL/pgSQL stores the result of the SELECT in a PL/pgSQL variable foo. Whereas SELECT ... INTO foo run as an ordinary SQL statement creates a table foo to store the result.
This is what caused the confusion, the table was created when I was testing the SQL statements from the trigger function manually against the DB.
I'm trying to create a Trigger/Function in Postgres that will check, upon an insert to a table, whether or not there is already another post by a different member with the same content. If there is a post, this function will not insert the new one and leave the table unchanged. Otherwise, it will be added.
So far, the trigger and function look like:
Trigger:
CREATE TRIGGER isPostUnique
AFTER INSERT ON posts
FOR EACH ROW
EXECUTE PROCEDURE deletePost();
Function:
CREATE FUNCTION deletePost() RETURNS TRIGGER AS $isPostUnique$
BEGIN
IF (EXISTS (SELECT * FROM posts p1, posts p2
WHERE (p1.userID <> p2.userID)
AND (p1.content LIKE p2.content)))
THEN
DELETE FROM NEW WHERE (posts.postID = NEW.postID);
RETURN NEW;
END IF;
END;
$isPostUnique$ LANGUAGE plpgsql;
Adding the function and trigger works without any errors, but when I try to run the following query to test it: INSERT INTO posts VALUES (7, 3, 'test redundant post', 10, 1); I get this error
ERROR: relation "new" does not exist
LINE 1: DELETE FROM NEW WHERE (posts.postID = NEW.postID)
^
QUERY: DELETE FROM NEW WHERE (posts.postID = NEW.postID)
CONTEXT: PL/pgSQL function dp() line 7 at SQL statement
I am aware that you can't use 'NEW' in FOR EACH ROW inserts, but I have no other idea of how to accomplish this.
Updated answer for updated question
Of course you can use NEW in FOR EACH ROW trigger function. You just can't direct a DELETE statement at it. It's a row type (data type HeapTuple to be precise), not a table.
To abort the INSERT silently (no exception raised) if the same content is already there ...
CREATE FUNCTION deletePost()
RETURNS TRIGGER AS
$func$
BEGIN
IF EXISTS (
SELECT 1
FROM posts p
WHERE p.content = NEW.content
-- AND p.userID <> NEW.userID -- I doubt you need this, too?
) THEN
RETURN NULL; -- cancel INSERT
ELSE
RETURN NEW; -- go ahead
END IF;
END
$func$ LANGUAGE plpgsql;
Of course this only works for a trigger ...
...
BEFORE INSERT ON posts
...
Unique index
A UNIQUE constraint or a unique index (almost the same effect) might be a superior solution:
CREATE UNIQUE INDEX posts_content_uni_idx (content);
Would raise an exception at the attempt to insert a duplicate value. No trigger necessary.
It also provides the very well needed index to speed up things.
I want to write a Postgres SQL trigger that will basically find if a number appears in a column 5 or more times. If it appears a 5th time, I want to throw an exception. Here is how the table looks:
create table tab(
first integer not null constraint pk_part_id primary key,
second integer constraint fk_super_part_id references bom,
price integer);
insert into tab values(1,NULL,100), (2,1,50), (3,1,30), (4,2,20), (5,2,10), (6,3,20);
Above are the original inserts into the table. My trigger will occur upon inserting more values into the table.
Basically if a number appears in the 'second' column more than 4 times after inserting into the table, I want to raise an exception. Here is my attempt at writing the trigger:
create function check() return trigger as '
begin
if(select first, second, price
from tab
where second in (
select second from tab
group by second
having count(second) > 4)
) then
raise exception ''Error, there are more than 5 parts.'';
end if;
return null;
end
'language plpgsql;
create trigger check
after insert or update on tab
for each row execute procedure check();
Could anyone help me out? If so that would be great! Thanks!
CREATE FUNCTION trg_upbef()
RETURN trigger as
$func$
BEGIN
IF (SELECT count(*)
FROM tab
WHERE second = NEW.second ) > 3 THEN
RAISE EXCEPTION 'Error: there are more than 5 parts.';
END IF;
RETURN NEW; -- must be NEW for BEFORE trigger
END
$func$ LANGUAGE plpgsql;
CREATE TRIGGER upbef
BEFORE INSERT OR UPDATE ON tab
FOR EACH ROW EXECUTE procedure trg_upbef();
Major points
Keyword is RETURNS, not RETURN.
Use the special variable NEW to refer to the newly inserted / updated row.
Use a BEFORE trigger. Better skip early in case of an exception.
Don't count everything for your test, just what you need. Much faster.
Use dollar-quoting. Makes your live easier.
Concurrency:
If you want to be absolutely sure, you'll have to take an exclusive lock on the table before counting. Else, concurrent inserts / updates might outfox each other under heavy concurrent load. While this is rather unlikely, it's possible.
Say we have a PostgreSQL table like so:
CREATE TABLE master (
id INT PRIMARY KEY,
...
);
and many other tables referencing it with foreign keys:
CREATE TABLE other (
id INT PRIMARY KEY,
id_master INT NOT NULL,
...
CONSTRAINT other_id_master_fkey FOREIGN KEY (id_master)
REFERENCES master (id) ON DELETE RESTRICT
);
Is there a way to check (from within trigger function) if a master row is deletable without actually trying to delete it? The obvious way is to do a SELECT on all referencing tables one by one, but I would like to know if there is an easier way.
The reason I need this is that I have a table with hierarchical data in which any row can have child rows, and only child rows that are lowest in hierarchy can be referenced by other tables. So when a row is about to become a parent row, I need to check whether it is already referenced anywhere. If it is, it cannot become a parent row, and insertion of new child row is denied.
You can try to delete the row and roll back the effects. You wouldn't want to do that in a trigger function because any exception cancels all persisted changes to the database. The manual:
When an error is caught by an EXCEPTION clause, the local variables of
the PL/pgSQL function remain as they were when the error occurred, but
all changes to persistent database state within the block are rolled back.
Bold emphasis mine.
But you can wrap this into a separate block or a separate plpgsql function and catch the exception there to prevent the effect on the main (trigger) function.
CREATE OR REPLACE FUNCTION f_can_del(_id int)
RETURNS boolean AS
$func$
BEGIN
DELETE FROM master WHERE master_id = _id; -- DELETE is always rolled back
IF NOT FOUND THEN
RETURN NULL; -- ID not found, return NULL
END IF;
RAISE SQLSTATE 'MYERR'; -- If DELETE, raise custom exception
EXCEPTION
WHEN FOREIGN_KEY_VIOLATION THEN
RETURN FALSE;
WHEN SQLSTATE 'MYERR' THEN
RETURN TRUE;
-- other exceptions are propagated as usual
END
$func$ LANGUAGE plpgsql;
This returns TRUE / FALSE / NULL indicating that the row can be deleted / not be deleted / does not exist.
db<>fiddle here
Old sqlfiddle
One could easily make this function dynamic to test any table / column / value.
Since PostgreSQL 9.2 you can also report back which table was blocking.
PostgreSQL 9.3 or later offer more detailed information, yet.
Generic function for arbitrary table, column and type
Why did the attempt on a dynamic function that you posted in the comments fail? This quote from the manual should give a clue:
Note in particular that EXECUTE changes the output of GET DIAGNOSTICS, but does not change FOUND.
It works with GET DIAGNOSTICS:
CREATE OR REPLACE FUNCTION f_can_del(_tbl regclass, _col text, _id int)
RETURNS boolean AS
$func$
DECLARE
_ct int; -- to receive count of deleted rows
BEGIN
EXECUTE format('DELETE FROM %s WHERE %I = $1', _tbl, _col)
USING _id; -- exception if other rows depend
GET DIAGNOSTICS _ct = ROW_COUNT;
IF _ct > 0 THEN
RAISE SQLSTATE 'MYERR'; -- If DELETE, raise custom exception
ELSE
RETURN NULL; -- ID not found, return NULL
END IF;
EXCEPTION
WHEN FOREIGN_KEY_VIOLATION THEN
RETURN FALSE;
WHEN SQLSTATE 'MYERR' THEN
RETURN TRUE;
-- other exceptions are propagated as usual
END
$func$ LANGUAGE plpgsql;
db<>fiddle here
Old sqlfiddle
While being at it, I made it completely dynamic, including the data type of the column (it has to match the given column, of course). I am using the polymorphic type anyelement for that purpose. See:
How to write a function that returns text or integer values?
I also use format() and a parameter of type regclass to safeguard against SQLi. See:
SQL injection in Postgres functions vs prepared queries
You can do that also with Procedure.
CREATE OR REPLACE procedure p_delable(_tbl text, _col text, _id int)
AS $$
DECLARE
_ct bigint;
_exists boolean; -- to receive count of deleted rows
BEGIN
_exists := (SELECT EXISTS ( SELECT FROM information_schema.tables
WHERE table_schema = 'public' AND table_name = $1 ));
IF _exists THEN
EXECUTE format('DELETE FROM %s WHERE %I = $1', _tbl, _col)
USING _id; -- exception if other rows depend
GET DIAGNOSTICS _ct = ROW_COUNT;
IF _ct > 0 THEN
RAISE SQLSTATE 'MYERR'; -- If DELETE, raise custom exception
ELSE
RAISE NOTICE 'no records found. no records will be deleted';
END IF;
ELSE
raise notice 'Input text is invalid table name.';
END IF;
EXCEPTION
WHEN undefined_column then
raise notice 'Input text is invalid column name.';
WHEN undefined_table then
raise notice 'Input text is invalid table name.';
WHEN FOREIGN_KEY_VIOLATION THEN
RAISE NOTICE 'foreign key violation, cannot be deleted.';
WHEN SQLSTATE 'MYERR' THEN
RAISE NOTICE 'rows % found and can be deleted.', _ct;
END
$$ LANGUAGE plpgsql;
You can call it, also can validate your input.
call p_delable('parent_tree', 'parent_id',30);
Will get:
NOTICE: no records found. no records will be deleted
Lets try an actual exist row.
call p_delable('parent_tree', 'parent_id',3);
It will return
NOTICE: rows 1 found and can be deleted.
It can also check your input table name exists in public schema or not.
call p_delable('parent_tre', 'parent_id',3);
It will give you notice:
NOTICE: Input text is invalid table name.