--- /dev/null
+
+Here are general trigger functions provided as workable examples
+of using SPI and triggers. "General" means that functions may be
+used for defining triggers for any tables but you have to specify
+table/field names (as described below) while creating a trigger.
+
+1. refint.c - functions for implementing referential integrity.
+
+check_primary_key () is to used for foreign keys of a table.
+
+ You are to create trigger (BEFORE INSERT OR UPDATE) using this
+function on a table referencing another table. You are to specify
+as function arguments: triggered table column names which correspond
+to foreign key, referenced table name and column names in referenced
+table which correspond to primary/unique key.
+ You may create as many triggers as you need - one trigger for
+one reference.
+
+check_foreign_key () is to used for primary/unique keys of a table.
+
+ You are to create trigger (BEFORE DELETE OR UPDATE) using this
+function on a table referenced by another table(s). You are to specify
+as function arguments: number of references for which function has to
+performe checking, action if referencing key found ('cascade' - to delete
+corresponding foreign key, 'restrict' - to abort transaction if foreign keys
+exist, 'setnull' - to set foreign key referencing primary/unique key
+being deleted to null), triggered table column names which correspond
+to primary/unique key, referencing table name and column names corresponding
+to foreign key (, ... - as many referencing tables/keys as specified
+by first argument).
+ Note, that NOT NULL constraint and unique index have to be defined
+by youself.
+
+ There are examples in refint.example and regression tests
+(sql/triggers.sql).
+
+
--- /dev/null
+--Column ID of table A is primary key:
+
+CREATE TABLE A (
+ ID int4 not null
+);
+CREATE UNIQUE INDEX AI ON A (ID);
+
+--Columns REFB of table B and REFC of C are foreign keys referenting ID of A:
+
+CREATE TABLE B (
+ REFB int4
+);
+CREATE INDEX BI ON B (REFB);
+
+CREATE TABLE C (
+ REFC int4
+);
+CREATE INDEX CI ON C (REFC);
+
+--Trigger for table A:
+
+CREATE TRIGGER AT BEFORE DELETE OR UPDATE ON A FOR EACH ROW
+EXECUTE PROCEDURE
+check_foreign_key (2, 'cascade', 'ID', 'B', 'REFB', 'C', 'REFC');
+/*
+2 - means that check must be performed for foreign keys of 2 tables.
+cascade - defines that corresponding keys must be deleted.
+ID - name of primary key column in triggered table (A). You may
+ use as many columns as you need.
+B - name of (first) table with foreign keys.
+REFB - name of foreign key column in this table. You may use as many
+ columns as you need, but number of key columns in referenced
+ table (A) must be the same.
+C - name of second table with foreign keys.
+REFC - name of foreign key column in this table.
+*/
+
+--Trigger for table B:
+
+CREATE TRIGGER BT BEFORE INSERT OR UPDATE ON B FOR EACH ROW
+EXECUTE PROCEDURE
+check_primary_key ('REFB', 'A', 'ID');
+
+/*
+REFB - name of foreign key column in triggered (B) table. You may use as
+ many columns as you need, but number of key columns in referenced
+ table must be the same.
+A - referenced table name.
+ID - name of primary key column in referenced table.
+*/
+
+--Trigger for table C:
+
+CREATE TRIGGER CT BEFORE INSERT OR UPDATE ON C FOR EACH ROW
+EXECUTE PROCEDURE
+check_primary_key ('REFC', 'A', 'ID');
+
+-- Now try
+
+INSERT INTO A VALUES (10);
+INSERT INTO A VALUES (20);
+INSERT INTO A VALUES (30);
+INSERT INTO A VALUES (40);
+INSERT INTO A VALUES (50);
+
+INSERT INTO B VALUES (1); -- invalid reference
+INSERT INTO B VALUES (10);
+INSERT INTO B VALUES (30);
+INSERT INTO B VALUES (30);
+
+INSERT INTO C VALUES (11); -- invalid reference
+INSERT INTO C VALUES (20);
+INSERT INTO C VALUES (20);
+INSERT INTO C VALUES (30);
+
+DELETE FROM A WHERE ID = 10;
+DELETE FROM A WHERE ID = 20;
+DELETE FROM A WHERE ID = 30;
+
+SELECT * FROM A;
+SELECT * FROM B;
+SELECT * FROM C;
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