INSERT problems: reference
Can't INSERT because of reference.
If a foreign key is set up between two tables it may be that you cannot insert unless a related record exists. In this example we cannot add ('Tom', 'ma') to t_staff table unless we first create a maths department ('ma', 'Mathematics') in the t_dept table.
CREATE TABLE t_dept(
id CHAR(2)
,fname VARCHAR(20)
,PRIMARY KEY(id));
CREATE TABLE t_staff(
name VARCHAR(20)
,dept CHAR(2)
,PRIMARY KEY(name)
,FOREIGN KEY(dept) REFERENCES t_dept(id))
DROP TABLE t_staff;
DROP TABLE t_dept;
CREATE TABLE t_dept(id CHAR(2), fname VARCHAR(20),PRIMARY KEY(id));
CREATE TABLE t_staff(name VARCHAR(20), dept CHAR(2),PRIMARY KEY(name),FOREIGN KEY(dept) REFERENCES t_dept(id));
INSERT INTO t_dept VALUES ('co','computing');
INSERT INTO t_staff VALUES ('andrew','co');
INSERT INTO t_staff VALUES ('tom', 'ma');
SELECT * FROM t_staff
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