I'm wondering if it's possible in postgresql to create an additional name for a table, such that the table can be referred to by either its new alias or the original name?
Like adding a view for the table, but which writes to the underlying table when you update or insert on the 'view'.
The purpose of this is to be able to rename a table without having to update all of the db clients at once (no downtime).
You can use Postgres RULES to do this.
Check out this article.
#CraigRinger mentions this answer:
CREATE VIEW alias_as_view as SELECT * FROM original_table;
CREATE FUNCTION write_to_underlying_table() RETURNS TRIGGER AS $$
BEGIN
IF TG_OP = 'INSERT' then
raise notice 'INSERT trigger, NEW = [%]', NEW;
ELSIF TG_OP = 'UPDATE' then
raise notice 'UPDATE trigger, OLD = [%], NEW = [%]', OLD, NEW;
ELSE
raise notice 'DELETE trigger, OLD = [%]', OLD;
END IF;
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER view_writable_trigger INSTEAD OF INSERT OR UPDATE OR DELETE
ON alias_as_view FOR EACH ROW EXECUTE PROCEDURE write_to_underlying_table();
I've rejected it for the moment as e.g. a failing query:
INSERT INTO alias_as_view VALUES ('existing_key', 'some_value');
Seems to have executed successfully, even though the actual INSERT statement on original_table failed due to a unique key violation.
Related
I am trying to create a trigger in postgres that if you are trying to add an existing id within a customers table it will raise an error and won't allow you to do it.
Trigger Code:
create trigger id_check()
before insert on customers
for each row execute procedure duplicates()
Function:
create or replace function duplicates()
returns trigger as $BODY$
begin
if exists(select 1 from customers where id = new.id)
then raise notice 'cannot have a duplicate id'
return new;
end;
$BODY$ LANGUAGE plpgsql;
I keep getting errors either and I'm not understanding what's wrong? Any help would be great.
As indicated a unique constraint is the appropriate method to properly handle this. But if you insist on your trigger then then you must cleanup the syntax errors: need semi-colon after raise statement, and end if at conclusion of IF. Also, learn now to format your code.
create or replace function duplicates()
returns trigger as $BODY$
begin
if exists(select 1 from customers where id = new.id)
then raise notice 'cannot have a duplicate id'; --- added ;
end if; --- added line
return new;
end;
$BODY$ LANGUAGE plpgsql;
I am trying to create a trigger and procedure to update a last_changed_timestamp column upon UPDATE and INSERT.
I can register the function and trigger just fine, but when I try to update a record I receive the error.
CREATE OR REPLACE FUNCTION update_my_table_last_changed_timestamp()
RETURNS trigger AS
$BODY$
BEGIN
UPDATE my_table SET NEW.last_changed_timestamp = NOW();
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql;
CREATE TRIGGER trigger_update_my_table_last_changed_timestamp
BEFORE UPDATE
ON my_table
FOR EACH ROW
EXECUTE PROCEDURE update_my_table_last_changed_timestamp();
column "new" of relation "my_table" does not exist
I also do not fully understand how update_my_table_last_changed_timestamp knows which row it's suppose to update, nor if there were parameters passed to it, how the I would get those variables from the trigger to the procedure.
Modify the NEW record, there is no need to update.
BEGIN
NEW.last_changed_timestamp = NOW();
RETURN NEW;
END;
Read in the documentation: Overview of Trigger Behavior
If you still want to access a (other )table in the update trigger.
You can add to beginning of your trigger body the following:
EXECUTE format('SET search_path TO %I', TG_TABLE_SCHEMA);
For some reason with the update trigger it can happen that you're not on the correct search_path (i believe some old psql version have this)
I want to create a trigger which counts rows and updates a field in an other table. My current solution works for INSERT statements but failes when I DELETE a row.
My current function:
CREATE OR REPLACE FUNCTION update_table_count()
RETURNS trigger AS
$$
DECLARE updatecount INT;
BEGIN
Select count(*) into updatecount
From source_table
Where id = new.id;
Update dest_table set count=updatecount
Where id = new.id;
RETURN NEW;
END;
$$
LANGUAGE 'plpgsql';
The trigger is a pretty basic one, looking like.
CREATE TRIGGER count_trigger
AFTER INSERT OR DELETE
ON source_table
FOR EACH ROW
EXECUTE PROCEDURE update_table_count();
When I excute a DELETE statement the following error occurs:
ERROR: record "new" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
I know one solution could be to create just one set of trigger and function for the DELETE and one for the INSERT statement. But I want to do it a bit more elegant and want to know, if there is a solution to check if NEW or OLD is present in the current context and just implement an IF ELSE block. But I dont know how to check for this context sensitive items.
Thanks for your help
The usual approach to make a trigger function do different things depending on how the trigger was fired is to check the trigger operation through TG_OP
CREATE OR REPLACE FUNCTION update_table_count()
RETURNS trigger AS
$$
DECLARE
updatecount INT;
BEGIN
if tg_op = 'UPDATE' then
select count(*) into updatecount from source_table where id = new.id;
update dest_table set count=updatecount where id = new.id;
elsif tg_op = 'DELETE' then
... do something else
end if;
RETURN NEW;
END;
$$
LANGUAGE plpgsql;
Unrelated, but: the language name is an identifier. Do not quote it using single quotes.
From PostgreSQL's documentation:
NEW
Data type RECORD; variable holding the new database row for INSERT/UPDATE operations in row-level triggers. This variable is null in statement-level triggers and for DELETE operations.
OLD
Data type RECORD; variable holding the old database row for UPDATE/DELETE operations in row-level triggers. This variable is null in statement-level triggers and for INSERT operations.
So, for example, if NEW is NULL, then the trigger was invoked on DELETE.
Need help to create a generic trigger to log all tables.
i have table named "system" and need to log it.
the log table name system_audit is created with all columns of "system" table along with additional three columns named
modified_dt,modified_by and modified_type.
modified_dt will be current_timestamp
modified_by will be the user
and modified_type specifies whether its insert,update or delete.(Need to capture new data for insert/update and old for delete)
How to write a function to capture the above said data. Also it needs to be dynamics, so that i can use it across all the tables in my schema
Note: All audit tables contains the modified_dt,modified_by and modified_type as mandatory.
I got a couple of codes from the net, but it is not working, I was working on with oracle before, and new to postgres, not sure on how to code it properly.Please help
I have managed to create a generic function and its working fine.Thanks for the help.
create or replace function audit.fn__audit()
returns trigger as
$func$
declare
col_name text:='';
audit_table_name text := TG_TABLE_NAME || '_audit';
begin
if TG_OP = 'UPDATE' or TG_OP = 'INSERT' THEN
EXECUTE format('INSERT INTO audit.%1$I SELECT ($1).*,current_timestamp,user,'''||TG_OP||'''',audit_table_name) using NEW;
else
EXECUTE format('INSERT INTO audit.%1$I SELECT ($1).*,current_timestamp,user,'''||TG_OP||'''',audit_table_name) using old;
end if;
return new;
END $func$
LANGUAGE plpgsql VOLATILE;
I've been playing around for the last hour or more trying to put an update statement into a trigger. I understand the concept of an UPDATE statement and the below works just fine
UPDATE cars SET country = 'France';
What I want is to put this into a trigger so that when the cars table is updated, the column country will automatically be updated with France.
I've played around with adapting Functions and Triggers that I've found out on the interweb but I'm obviously making the statement wrong as either they don't execute or they execute but don't update the country field when a new record is added.
CREATE FUNCTION update_country () RETURNS TRIGGER AS $$
BEGIN
IF (TG_OP = 'UPDATE') THEN
UPDATE cars SET country = 'France' WHERE id = New.id;
END IF;
RETURN NULL;
END;
$$ LANGUAGE plpgsql; --The trigger used to update a table.
CREATE TRIGGER update_country_col BEFORE UPDATE ON cars FOR EACH ROW EXECUTE PROCEDURE update_country();
The above scripts executes but does not add France to the country column.
The function was adapted from a statement that I found out on the web.
Postgres 9.1.
I know that the answer is going to be so simple!
In update triggers you should modify NEW record.
Also, you may need to return NEW record from procedure.
So, you should use following procedure instead of yours:
CREATE FUNCTION update_country () RETURNS TRIGGER AS $$
BEGIN
IF (TG_OP = 'UPDATE') THEN
NEW.country = 'France';
END IF;
RETURN NEW;
END; $$ LANGUAGE plpgsql;