CREATE DATABASE rgipt;
USE rgipt;

CREATE TABLE t3 (
    department_name VARCHAR(20) PRIMARY KEY
);
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CREATE TABLE t2 (
    dept_name VARCHAR(20) PRIMARY KEY,
    salary INT,
    FOREIGN KEY (dept_name) REFERENCES t3(department_name)
);
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CREATE TABLE t1 (
	id INT PRIMARY KEY,
    d_name VARCHAR(20),
    FOREIGN KEY (d_name) REFERENCES t2(dept_name)
);
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INSERT INTO t3 VALUES ('CSE');
INSERT INTO t3 VALUES ('ECE');
-------------------------------------------------------
INSERT INTO t2 VALUES ('CSE', 10);
INSERT INTO t2 VALUES ('ECE', 20);
INSERT INTO t2 VALUES ('CSE', 10);   Duplicate entry 'CSE' for key 't2.PRIMARY'
INSERT INTO t2 VALUES ('EE', 10); 	 Cannot add or update a child row: a foreign key constraint fails