How to avoid UPDATE on same data in table ?
Hello, I'm using PostgreSQL 12.1 and trying to avoid update on table when data is the same. I read somewhere if UPDATE is with the same data SQL server on system level does not do update on table but don't know if that is true or not. If that is not true I do: First I create a function that should update data: CREATE OR REPLACE FUNCTION log_last_chaged() RETURNS TRIGGER LANGUAGE plpgsql AS $$ BEGIN UPDATE status_table SET status0 = NEW.status0, lastchage = CURRENT_TIMESTAMP WHERE rowid = OLD.rowid; RETURN NEW; END $$; then create table: CREATE TABLE status_table ( rowid INTEGER, status0 INTEGER, lastchage TIMESTAMP(0) WITHOUT TIME ZONE ); attach trigger: DROP TRIGGER last_changes ON card_sync_tbl; CREATE TRIGGER last_changes BEFORE UPDATE ON status_table FOR EACH ROW WHEN (OLD.* IS DISTINCT FROM NEW.*) EXECUTE FUNCTION log_last_chaged(); insert first data: INSERT INTO status_table (rowid, status0) VALUES (11, 1); INSERT INTO status_table (rowid, status0) VALUES (12, 2); and check do everything work fine: UPDATE status_table SET status0 = 1 WHERE rowid = 11; UPDATE status_table SET status0 = 4 WHERE rowid = 12; I receive something on rowid 12 that probably is error: SQL statement "UPDATE status_table SET status0 = NEW.status0, lastchage = CURRENT_TIMESTAMP WHERE rowid = OLD.rowid" PL/pgSQL function log_last_chaged() line 3 at SQL statement After quick look on duckduckgo I change the function to this: CREATE OR REPLACE FUNCTION log_last_chaged() RETURNS TRIGGER LANGUAGE plpgsql AS $$ BEGIN NEW.lastchage := CURRENT_TIMESTAMP; RETURN NEW; END $$; and everything seems work now, but that break the idea update not to hit table if data is the same. Any body can help with some hint ? Also I want to know why my first function does not work, probably loop is happened if trigger does not stop update to be sent to table on rowid 12 or syntax error. Regards, HS
Re: How to avoid UPDATE on same data in table ?
Am 02.02.20 um 10:24 schrieb Condor: CREATE TRIGGER last_changes BEFORE UPDATE ON status_table FOR EACH ROW WHEN (OLD.* IS DISTINCT FROM NEW.*) try to exclude the column lastchange from the comparison. Andreas -- 2ndQuadrant - The PostgreSQL Support Company. www.2ndQuadrant.com
Re: How to avoid UPDATE on same data in table ?
Am 02.02.20 um 14:37 schrieb Andreas Kretschmer: Am 02.02.20 um 10:24 schrieb Condor: CREATE TRIGGER last_changes BEFORE UPDATE ON status_table FOR EACH ROW WHEN (OLD.* IS DISTINCT FROM NEW.*) try to exclude the column lastchange from the comparison. test=*# select ctid, * from status_table ; ctid | rowid | status0 | lastchage ---+---+-+- (0,3) | 11 | 1 | (0,5) | 12 | 4 | 2020-02-02 15:40:42 (2 rows) test=*# UPDATE status_table SET status0 = 4 WHERE rowid = 12; UPDATE 1 test=*# commit; COMMIT test=# select ctid, * from status_table ; ctid | rowid | status0 | lastchage ---+---+-+- (0,3) | 11 | 1 | (0,6) | 12 | 4 | 2020-02-02 15:40:42 (2 rows) test=*# \d status_table Table "public.status_table" Column | Type | Collation | Nullable | Default ---++---+--+- rowid | integer | | | status0 | integer | | | lastchage | timestamp(0) without time zone | | | Triggers: last_changes BEFORE UPDATE ON status_table FOR EACH ROW WHEN (old.rowid IS DISTINCT FROM new.rowid OR old.status0 IS DISTINCT FROM new.status0) EXECUTE FUNCTION log_last_changed() Andreas -- 2ndQuadrant - The PostgreSQL Support Company. www.2ndQuadrant.com
Re: How to avoid UPDATE on same data in table ?
Condor writes: > I'm using PostgreSQL 12.1 and trying to avoid update on table when data > is the same. I read somewhere if UPDATE is with the same data SQL server > on system level does not do update on table but don't know if that is > true or not. It is not, at least not for PG (can't say about SQL Server). But see suppress_redundant_updates_trigger here: https://www.postgresql.org/docs/current/functions-trigger.html regards, tom lane
Re: How to avoid UPDATE on same data in table ?
Am 02.02.20 um 18:18 schrieb Tom Lane: https://www.postgresql.org/docs/current/functions-trigger.html regards, tom lane cool. Andreas -- 2ndQuadrant - The PostgreSQL Support Company. www.2ndQuadrant.com
Re: How to avoid UPDATE on same data in table ?
On 2/2/20 1:24 AM, Condor wrote: Hello, I'm using PostgreSQL 12.1 and trying to avoid update on table when data is the same. I read somewhere if UPDATE is with the same data SQL server on system level does not do update on table but don't know if that is true or not. If that is not true I do: First I create a function that should update data: CREATE OR REPLACE FUNCTION log_last_chaged() RETURNS TRIGGER LANGUAGE plpgsql AS $$ BEGIN UPDATE status_table SET status0 = NEW.status0, lastchage = CURRENT_TIMESTAMP WHERE rowid = OLD.rowid; RETURN NEW; END $$; then create table: CREATE TABLE status_table ( rowid INTEGER, status0 INTEGER, lastchage TIMESTAMP(0) WITHOUT TIME ZONE ); attach trigger: Why the DROP TRIGGER on card_sync_tbl? More below. DROP TRIGGER last_changes ON card_sync_tbl; CREATE TRIGGER last_changes BEFORE UPDATE ON status_table FOR EACH ROW WHEN (OLD.* IS DISTINCT FROM NEW.*) EXECUTE FUNCTION log_last_chaged(); insert first data: INSERT INTO status_table (rowid, status0) VALUES (11, 1); INSERT INTO status_table (rowid, status0) VALUES (12, 2); and check do everything work fine: UPDATE status_table SET status0 = 1 WHERE rowid = 11; UPDATE status_table SET status0 = 4 WHERE rowid = 12; I receive something on rowid 12 that probably is error: SQL statement "UPDATE status_table SET status0 = NEW.status0, lastchage = CURRENT_TIMESTAMP WHERE rowid = OLD.rowid" PL/pgSQL function log_last_chaged() line 3 at SQL statement After quick look on duckduckgo I change the function to this: CREATE OR REPLACE FUNCTION log_last_chaged() RETURNS TRIGGER LANGUAGE plpgsql AS $$ BEGIN NEW.lastchage := CURRENT_TIMESTAMP; RETURN NEW; END $$; and everything seems work now, but that break the idea update not to hit table if data is the same. Some changes based on: https://www.postgresql.org/docs/12/sql-createtrigger.html "In a BEFORE trigger, the WHEN condition is evaluated just before the function is or would be executed, so using WHEN is not materially different from testing the same condition at the beginning of the trigger function. Note in particular that the NEW row seen by the condition is the current value, as possibly modified by earlier triggers. " https://www.postgresql.org/docs/12/plpgsql-trigger.html#PLPGSQL-DML-TRIGGER "Row-level triggers fired BEFORE can return null to signal the trigger manager to skip the rest of the operation for this row (i.e., subsequent triggers are not fired, and the INSERT/UPDATE/DELETE does not occur for this row)." CREATE OR REPLACE FUNCTION public.log_last_chaged() RETURNS trigger LANGUAGE plpgsql AS $function$ BEGIN IF OLD.* IS DISTINCT FROM NEW.* THEN RAISE NOTICE 'UPDATE'; NEW.lastchage := CURRENT_TIMESTAMP; RETURN NEW; ELSE RETURN NULL; END IF; END $function$ CREATE TRIGGER last_changes BEFORE UPDATE ON status_table FOR EACH ROW EXECUTE FUNCTION log_last_chaged(); test=> INSERT INTO status_table (rowid, status0) VALUES (11, 1); INSERT 0 1 test=> INSERT INTO status_table (rowid, status0) VALUES (12, 2); INSERT 0 1 test=> select ctid, * from status_table ; ctid | rowid | status0 | lastchage ---+---+-+--- (0,1) |11 | 1 | (0,2) |12 | 2 | (2 rows) test=> UPDATE status_table SET status0 = 1 WHERE rowid = 11; UPDATE 0 test=> select ctid, * from status_table ; ctid | rowid | status0 | lastchage ---+---+-+--- (0,1) |11 | 1 | (0,2) |12 | 2 | (2 rows) NOTE: UPDATE 0 and no change in ctid test=> UPDATE status_table SET status0 = 4 WHERE rowid = 12; NOTICE: UPDATE UPDATE 1 test=> select ctid, * from status_table ; ctid | rowid | status0 | lastchage ---+---+-+- (0,1) |11 | 1 | (0,3) |12 | 4 | 02/02/2020 13:03:21 (2 rows) NOTE: UPDATE 1 and ctid change. Any body can help with some hint ? Also I want to know why my first function does not work, probably loop is happened if trigger does not stop update to be sent to table on rowid 12 or syntax error. Regards, HS -- Adrian Klaver adrian.kla...@aklaver.com
Restrict connection from pgadmin.
Hi All, Is there any way to restrict the connection only from pgadmin??? The same user can connect through application but can't from pgadmin.. Or any logon triggers..???
