How can I create triggers for a postgreSQL db using liquibase? - postgresql

Question

I'm using the dropwizard-migrations module for liquibase db refactoring. See the guide here: http://dropwizard.codahale.com/manual/migrations/
When I run
java -jar my_project.jar db migrate my_project.yml
I get the following error:
ERROR [2013-09-11 20:53:43,089] liquibase: Change Set migrations.xml::11::me failed. Error: Error executing SQL CREATE OR REPLACE TRIGGER add_current_date_to_my_table BEFORE UPDATE ON my_table FOR EACH ROW EXECUTE PROCEDURE change_update_time();: ERROR: syntax error at or near "TRIGGER"
Position: 19
Here are some relevant changesets from my migrations.xml file:
<changeSet id="1" author="me">
<createProcedure>
CREATE OR REPLACE FUNCTION change_update_time() RETURNS trigger
LANGUAGE plpgsql
AS $$
BEGIN
NEW.updated_at := CURRENT_TIMESTAMP;
RETURN NEW;
END;
$$;
</createProcedure>
<rollback>
DROP FUNCTION change_update_time();
</rollback>
</changeSet>
<changeSet id="2" author="me">
<preConditions>
<not>
<tableExists tableName="my_table"/>
</not>
</preConditions>
<createTable tableName="my_table">
<column name="_id" type="integer" defaultValue="0">
<constraints nullable="false"/>
</column>
<column name="updated_at" type="timestamp without time zone" defaultValue="now()">
<constraints nullable="false"/>
</column>
</createTable>
</changeSet>
<changeSet id="3" author="me">
<sql splitStatements="false">
CREATE OR REPLACE TRIGGER add_current_date_to_my_table BEFORE UPDATE ON my_table FOR EACH ROW EXECUTE PROCEDURE change_update_time();
</sql>
<rollback>
DROP TRIGGER add_current_date_to_my_table ON my_table;
</rollback>
</changeSet>
Is there any way I can create the trigger add_current_date_to_my_table? Is this redundant with the "RETURNS trigger" from creating the function?

Answer 1

The solution is:
<changeSet id="3" author="me">
<sql>
DROP TRIGGER IF EXISTS add_current_date_to_my_table ON my_table;
CREATE TRIGGER add_current_date_to_my_table BEFORE UPDATE ON my_table FOR EACH ROW EXECUTE PROCEDURE change_update_time();
</sql>
<rollback>
DROP TRIGGER add_current_date_to_my_table ON my_table;
</rollback>
</changeSet>
H/T Jens.

Answer 2

Ann Kilzer has provided the right answer as there is no CREATE OR REPLACE statement in Postgres, unlike PL/SQL.
So we need to split this statement into 2 atomic operations:
DROP TRIGGER
CREATE TRIGGER