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SQL command to create relations between tables
I everybody!
Does anybody know which is the SQL command to create relations between tables?
Thank you very much!
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/* create 2 tables named PARENT and CHILD */
CREATE TABLE parent( pfield1 int, pfileld2 char (30) );
CREATE TABLE child ( cfield1 int, cfied2 char(20), cfield3 int );
/* create the primary key for PARENT and CHILD, this field will represent a unique identifier for each of the table */
ALTER TABLE parent add (primary key(pfield1));
ALTER TABLE child add (primary key(cfield1));
/* create the relation between PARENT and CHILD */
ALTER TABLE child ADD ( FOREIGN KEY (cfield3) REFERENCES parent(pfield1));
/* Insert data into parent and child tables */
INSERT INTO parent values(1,'first row');
INSERT INTO parent values(2,'2nd row');
INSERT INTO parent values(3,'tird row');
INSERT INTO child values(1,'first child',2);
INSERT INTO child values(2,'2nd child',2);
INSERT INTO child values(3,'third child',1);
INSERT INTO child values(4,'4th child',1);
/* make a query using relations */
SELECT * FROM parent,child
where parent.pfield1=child.cfield3
Good luck in you lesson !
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