| Server IP : 85.214.239.14 / Your IP : 3.137.214.16 Web Server : Apache/2.4.62 (Debian) System : Linux h2886529.stratoserver.net 4.9.0 #1 SMP Tue Jan 9 19:45:01 MSK 2024 x86_64 User : www-data ( 33) PHP Version : 7.4.18 Disable Function : pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,pcntl_unshare, MySQL : OFF | cURL : OFF | WGET : ON | Perl : ON | Python : ON | Sudo : ON | Pkexec : OFF Directory : /proc/2/task/2/cwd/proc/3/cwd/usr/share/doc/postgresql-15/examples/ |
Upload File : |
--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 referencing 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;