I have successfully set up a history table according to this tutorial:
https://www.cybertec-postgresql.com/en/tracking-changes-in-postgresql/
My problem is that this function saves both the whole new record and the whole old record as jsons.
How can I alter this function so that only those column titles and values will be added to the json, which have really been changed?
In other words how can I replace the expression 'row_to_json(OLD)' with one which represents only the difference between row_to_json(NEW) row_to_json(OLD)?
CREATE FUNCTION change_trigger() RETURNS trigger AS $$
BEGIN
IF TG_OP = 'INSERT'
THEN
INSERT INTO logging.t_history (tabname, schemaname, operation, new_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP, row_to_json(NEW));
RETURN NEW;
ELSIF TG_OP = 'UPDATE'
THEN
INSERT INTO logging.t_history (tabname, schemaname, operation, new_val, old_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP,
row_to_json(NEW), row_to_json(OLD));
RETURN NEW;
ELSIF TG_OP = 'DELETE'
THEN
INSERT INTO logging.t_history (tabname, schemaname, operation, old_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP, row_to_json(OLD));
RETURN OLD;
END IF;
END;
$$ LANGUAGE 'plpgsql' SECURITY DEFINER;
Finally figured out that
I needed to convert the 'NEW' and 'OLD' rows to jsonb. (to_jsonb(NEW))
I needed another function which does the subtraction
https://coussej.github.io/2016/05/24/A-Minus-Operator-For-PostgreSQLs-JSONB/
Related
I am new with mysql triggers, I have 2 tables in a database, one is called tasks and the other is task_rules.
Once a new task_rule is inserted, I want to compare the field time (which is a time object) to the current time.
if it is greater than the current time, I want to add a new row in tasks and set rid (in tasks) to id of the newly added rule, and the time field in tasks to the time field of the newly added row.
I am getting many syntax errors and i didnt know how to create this trigger.
BEGIN
DECLARE #time TIME
DECLARE #freq VARCHAR(400)
#time = NEW.time
#freq = NEW.frequency
IF (#time > NOW()) AND (#freq == 'daily') THEN
INSERT INTO task_rules ('rid', 'time') VALUES (NEW.id, #time)
END IF
END
Im doing it using phpmyadmin
1) user defined variable (those preceded with #) should not be declared see How to declare a variable in MySQL? 2) to assign a value to a variable you have to use the SET statement 3) every statement must be terminated - if you are using phpmyadmin and the default terminator is set to ; change it and terminate your statements in the trigger with ; see - https://dev.mysql.com/doc/refman/8.0/en/stored-programs-defining.html 4) null safe equals in mysql is not == from memory this should be <=> see https://dev.mysql.com/doc/refman/8.0/en/comparison-operators.html 5) you should probably set delimiters before and after the trigger 6) column names should be escaped with back ticks not single quotes. 7) for each row clause missing before begin statement.
try this
drop trigger if exists t;
delimiter $$
create trigger t after insert on task
for each row
BEGIN
DECLARE vtime TIME;
DECLARE vfreq VARCHAR(400);
set time = NEW.time;
set freq = NEW.frequency;
IF (vtime > NOW()) AND (vfreq <=> 'daily') THEN
INSERT INTO task_rules (`rid`, `time`) VALUES (NEW.id, vtime);
END IF;
END $$
delimiter ;
And do review https://dev.mysql.com/doc/refman/8.0/en/trigger-syntax.html
Since SQL does not have a FOR-EACH statement, how could we verify if there is a difference on each value from the OLD object to the NEW object in a AFTER UPDATE type TRIGGER without knowing the table columns [and table names]?
Example today:
CREATE TRIGGER `audit_events_ugly`
AFTER UPDATE ON `accounts`
FOR EACH ROW
BEGIN
DECLARE changes VARCHAR(8000);
IF OLD.user_name <> NEW.user_name THEN
SET changes = 'user_name from % to %';
END IF;
IF OLD.user_type <> NEW.user_type THEN
SET changes = CONCAT(changes, ', user_type from % to %');
END IF;
IF OLD.user_email <> NEW.user_email THEN
SET changes = CONCAT(changes, ', user_email from % to %');
END IF;
CALL reg_event(how_canI_get_tableName?, #user_id, changes);
-- and that can go on and on... differently for every table.
END;
Example as I wish it could be:
CREATE TRIGGER `audit_events_nice`
AFTER UPDATE ON `accounts`
FOR EACH ROW
BEGIN
DECLARE changes VARCHAR(8000);
DECLARE N INT DEFAULT 1;
FOREACH OLD, NEW as OldValue, NewValue
BEGIN
IF OldValue <> NewValue THEN
SET changes = CONCAT(changes, ', column N: % to %');
SET N = N + 1;
END IF;
CALL reg_event(how_canI_get_tableName?, #user_id, changes);
-- now I can paste this code in every table that is audited..
END;
Any Ideas? WHILE, FOREACH, ARRAYS...
I think you cannot do that directly in a for-loop at the trigger level.
However, you could use a script to generate the trigger code. You would need to re-generate it every time you add/remove a field to the table (usually not frequently).
I am Using Mysql DB. my question is : can i create array using sql?
if Yes then how and how to populate this array with output of following query -- "Select column_name1 From tableName".
Help me, Thanks in Advance
As I mentioned in my comment, MySQL does not support arrays by itself. That kind of structures are supported by other programming languages (like PHP, Java, Python, etcetera) and you can write a program capable of connecting to a MySQL database, read data from it and populate arrays (I think PostgreSQL supports an array data type, but I'm not sure).
What you can do is use cursors in a stored procedure to retreive data from a query and store it into variables.
Example:
delimiter $$
create procedure my_procedure()
begin
declare value varchar(100);
declare done int default false;
declare cur cursor for
select column_name1 from your_table;
declare continue handler for not found set done = true;
open cur; -- This line will open the row set and place the cursor
-- on the first row.
loop_data: loop
fetch cur into value; -- This line will fetch the current row
-- into the variable and move the cursor
-- to the next row.
if done then -- If there are no more rows in the
leave loop_data; -- row set, the loop is terminated here
end if; -- and the execution moves to the next
-- instruction after "end loop;"
-- do whatever you need to do with the retrieved value
end loop;
close cur;
end $$
delimiter ;
If you want to use an array in a high level programming language, you can do it using the appropriate methods. Here's an example using Java (read The Java tutorials: JDBC Database access for more info):
public class SomeClass {
/*
Retrieve data from a database and return an array with it.
Parameters:
- conn: Connection to the database.
*/
public String[] getValues(Connection conn) {
String[] ans = new String[10];
int i;
try(
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(
"select column_name1 from your_table limit 10"
);
) {
rs.beforeFirst();
i = 0;
while(rs.next()) {
ans[i] = rs.getString("column_name1");
i++;
}
} catch(SQLException e) {
// Code to handle the SQL exception
}
return ans;
}
}
References:
MySQL reference manual: Cursors
You can use an variable to simply select your row values into a string. Not precisely an array, but it allows you to store all your values into a single variable:
-- load test data
create table tableName (column_name1 varchar(5));
insert into tableName values
('abcde');
insert into tableName values
('fghij');
insert into tableName values
('klmno');
insert into tableName values
('pqrst');
insert into tableName values
('uvwzy');
insert into tableName values
('z');
-- build "array"
set #array := '';
select #array := concat(#array,column_name1) as array
from tableName;
select #array;
I have two tables: table1 and table2, which triggers on inserts and on updates in the same function.
As you insert a value in table1 or table2 a value is inserted in table3, with the value table1.lastname || table1.firstname assigned to column3. The id obtained for the insert in table3 must be inserted into table1.id_table3.
CREATE OR REPLACE FUNCTION myschema.myfunction() RETURNS trigger AS
$BODY$
DECLARE
new_id_table_4 integer;
BEGIN
IF TG_OP = 'INSERT' THEN
IF TG_TABLE_NAME = 'table1' THEN
new_id_table_4 := 1;
ELSIF TG_TABLE_NAME = 'table2' THEN
new_id_table_4 := 2;
END IF;
INSERT INTO myschema.table3
(id, id_table4, name)
VALUES (DEFAULT, new_id_table_4, NEW.columnA||', '||NEW.columnB, TRUE, TRUE)
RETURNING id
INTO NEW.id_table3;
ELSIF TG_OP = 'UPDATE' THEN
IF OLD.columnA <> NEW.columnA OR OLD.columnB <> NEW.columnB THEN
UPDATE myschema.table3 SET
name = NEW.columnA||', '||NEW.columnB
WHERE id = NEW.id_cuenta;
END IF;
END IF;
RETURN NEW;
END
$BODY$
LANGUAGE plpgsql VOLATILE COST 100;
ALTER FUNCTION myschema.myfunction() OWNER TO myuser;
CREATE TRIGGER add_table3record_table1
AFTER INSERT OR UPDATE
ON myschema.table1
FOR EACH ROW
EXECUTE PROCEDURE myschema.myfunction();
CREATE TRIGGER add_table3record_table2
AFTER INSERT OR UPDATE
ON myschema.table2
FOR EACH ROW
EXECUTE PROCEDURE myschema.myfunction();
The problem is that when I insert a new record into table1 or table2,
...RETURNING id INTO NEW.id_table3;
It does not seem to have any effect.
This is my first function/trigger ever, and I cannot find the error.
Thank you!
I'm pretty sure you can't update a row AFTER it has already been inserted just by setting NEW.foo = bar.
Either:
Perform an update on the table1 setting the new id_table3 value (which is going to recursively call you ON UPDATE trigger, so be careful), or
Use a BEFORE trigger instead of an AFTER.
Depending on how your foreign keys are set up between table1 and table3, the latter may or may not be an option.
I've an UPSERT trigger on a table that may update instead of inserting while doing insert operation. I've function doing insert on that table and returning id However it doesn't return an id when it updates instead of inserting. I want to get the id in both cases.
Trigger Code
perform 1 from tera_subject
where id = new.subject_id and owner = new.user_id;
if found then
return null;
else
select id into vote_id from tera_votes where
user_id = new.user_id and
subject_id = new.subject_id;
if not found then
return new;
else
-- raise notice 'vote_id: % ; vote: %',vote_id,new.vote;
if(tg_op = 'INSERT') then
begin
-- raise notice 'redirecting to update';
update tera_votes
set vote=new.vote
WHERE id = vote_id;
end;
elsif(tg_op = 'UPDATE') then
-- raise notice 'in update';
return new;
end if;
-- raise notice 'end of trigger %',tg_op;
return null;
end if;
end if;
end;
I don't think you'll manage to have anything “returned” by the trigger.
What you're doing inside is:
running update based on your conditions;
suppressing the INSERT statement that fired the trigger.
This means, that INSERT is terminated in an easy way (without exception), but it also means that it's impossible to provide you any details, as trigger functions do not return any values.
If you need to have the ID of the UPSERT-ed item, consider using a function that will always return you the ID, like this one.