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83 lines
2.1 KiB
Plaintext
83 lines
2.1 KiB
Plaintext
--Column ID of table A is primary key:
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CREATE TABLE A (
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ID int4 not null
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);
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CREATE UNIQUE INDEX AI ON A (ID);
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--Columns REFB of table B and REFC of C are foreign keys referenting ID of A:
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CREATE TABLE B (
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REFB int4
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);
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CREATE INDEX BI ON B (REFB);
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CREATE TABLE C (
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REFC int4
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);
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CREATE INDEX CI ON C (REFC);
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--Trigger for table A:
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CREATE TRIGGER AT BEFORE DELETE OR UPDATE ON A FOR EACH ROW
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EXECUTE PROCEDURE
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check_foreign_key (2, 'cascade', 'ID', 'B', 'REFB', 'C', 'REFC');
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/*
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2 - means that check must be performed for foreign keys of 2 tables.
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cascade - defines that corresponding keys must be deleted.
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ID - name of primary key column in triggered table (A). You may
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use as many columns as you need.
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B - name of (first) table with foreign keys.
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REFB - name of foreign key column in this table. You may use as many
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columns as you need, but number of key columns in referenced
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table (A) must be the same.
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C - name of second table with foreign keys.
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REFC - name of foreign key column in this table.
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*/
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--Trigger for table B:
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CREATE TRIGGER BT BEFORE INSERT OR UPDATE ON B FOR EACH ROW
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EXECUTE PROCEDURE
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check_primary_key ('REFB', 'A', 'ID');
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/*
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REFB - name of foreign key column in triggered (B) table. You may use as
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many columns as you need, but number of key columns in referenced
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table must be the same.
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A - referenced table name.
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ID - name of primary key column in referenced table.
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*/
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--Trigger for table C:
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CREATE TRIGGER CT BEFORE INSERT OR UPDATE ON C FOR EACH ROW
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EXECUTE PROCEDURE
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check_primary_key ('REFC', 'A', 'ID');
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-- Now try
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INSERT INTO A VALUES (10);
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INSERT INTO A VALUES (20);
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INSERT INTO A VALUES (30);
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INSERT INTO A VALUES (40);
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INSERT INTO A VALUES (50);
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INSERT INTO B VALUES (1); -- invalid reference
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INSERT INTO B VALUES (10);
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INSERT INTO B VALUES (30);
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INSERT INTO B VALUES (30);
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INSERT INTO C VALUES (11); -- invalid reference
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INSERT INTO C VALUES (20);
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INSERT INTO C VALUES (20);
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INSERT INTO C VALUES (30);
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DELETE FROM A WHERE ID = 10;
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DELETE FROM A WHERE ID = 20;
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DELETE FROM A WHERE ID = 30;
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SELECT * FROM A;
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SELECT * FROM B;
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SELECT * FROM C;
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