I'm looking for a way to script postgreSQL schema changes in an idempotent manner.
In MSSQL I could do something like this:
if(not exists(select * from information_schema.columns where table_name = 'x' and column_name = 'y')) begin alter table x add y int end go
PostgreSQL doesn't seem to allow ad-hoc pl/pgsql in the same way MSSQL does with T-SQL so I can't use control structures in a SQL script and run it with psql -f x.sql.
I know PostgreSQL will throw an error if the object already exists but I don't want to have to ignore errors.
I could use some schema versioning technique like dbdeploy but I really like the simplicity of running a set of files through psql without incurring any unwanted side effects.
Is this possible?
Thanks, Mark
Disclaimer: I know, this is a very old question and already has an accepted answer.
But I'd like to register here a totally idempotent script, without external links.
A simple script demonstrating PostgreSQL 9.5+ idempotent built-in capabilities. You can run this script as many times as you wish. Here we go:
--Table CREATE TABLE IF NOT EXISTS person ( id integer NOT NULL, person_name character varying(40) NOT NULL, updated_date date, CONSTRAINT person_pkey PRIMARY KEY (id) ); --Index CREATE INDEX IF NOT EXISTS idx_person_name ON person (person_name); --Sequence CREATE SEQUENCE IF NOT EXISTS seq_person_inc; --Function CREATE OR REPLACE FUNCTION simple_sum(a_integer int, b_integer int) RETURNS INT AS $$ SELECT a_integer+b_integer $$ LANGUAGE SQL; --View CREATE OR REPLACE VIEW vw_select_1 AS SELECT 1; --Role DO $$ BEGIN CREATE ROLE rick_deckard; EXCEPTION WHEN duplicate_object THEN RAISE NOTICE 'Role already exists. Ignoring...'; END$$; --Simple insert INSERT INTO person (id, person_name) VALUES (1, 'HAL-9000'); --Upsert (insert + update) INSERT INTO person (id, person_name) VALUES (1, 'Betrayer') ON CONFLICT ON CONSTRAINT person_pkey DO UPDATE SET person_name = EXCLUDED.person_name; --Upsert (ignoring duplicate error) INSERT INTO person (id, person_name) VALUES (1, 'HAL-9000') ON CONFLICT ON CONSTRAINT person_pkey DO NOTHING; --Upsert (ignoring any error) INSERT INTO person (id, person_name) VALUES (1, 'HAL-9000') ON CONFLICT DO NOTHING; --Field DO $$ BEGIN ALTER TABLE person ADD COLUMN id_another_person INTEGER; EXCEPTION WHEN duplicate_column THEN RAISE NOTICE 'Field already exists. Ignoring...'; END$$; --Constraint DO $$ BEGIN ALTER TABLE person ADD CONSTRAINT person_id_another_person_fkey FOREIGN KEY (id_another_person) REFERENCES person (id); EXCEPTION WHEN duplicate_object THEN RAISE NOTICE 'Constraint already exists. Ignoring...'; END$$; --Trigger CREATE OR REPLACE FUNCTION person_trigger_function() RETURNS trigger AS $BODY$ BEGIN --Something complex here =) RETURN NEW; END; $BODY$ LANGUAGE plpgsql; DO $$ BEGIN CREATE TRIGGER person_trigger BEFORE INSERT OR UPDATE ON person FOR EACH ROW EXECUTE PROCEDURE person_trigger_function(); EXCEPTION WHEN duplicate_object THEN RAISE NOTICE 'Trigger already exists. Ignoring...'; END$$; --Drop DROP TRIGGER IF EXISTS person_trigger ON person; DROP INDEX IF EXISTS idx_person_name; ALTER TABLE person DROP COLUMN IF EXISTS person_name; ALTER TABLE person DROP CONSTRAINT IF EXISTS person_id_another_person_fkey; DROP ROLE IF EXISTS rick_deckard; DROP VIEW IF EXISTS vw_select_1; DROP FUNCTION IF EXISTS simple_sum(integer, integer); DROP FUNCTION IF EXISTS person_trigger_function(); DROP TABLE IF EXISTS person; DROP SEQUENCE IF EXISTS seq_person_inc;
You should be able to use plpgsql:
create language plpgsql; create function f() ... as $$ <plpgsql code> $$language plpgsql; select f();
