How would you add a foreign key constraint on the dept_no column in the EMP table, referring to the id column in the DEPT table?Select one:a.Use the ALTER TABLE command with the MODIFY clause on the DEPT table.b.This task cannot be accomplished.c.Use the ALTER TABLE command with the MODIFY clause on the EMP table.d.Use the ALTER TABLE command with the ADD clause on the EMP table.e.Use the ALTER TABLE command with the MODIFY clause on the EMP table.
Question
How would you add a foreign key constraint on the dept_no column in the EMP table, referring to the id column in the DEPT table?Select one:a.Use the ALTER TABLE command with the MODIFY clause on the DEPT table.b.This task cannot be accomplished.c.Use the ALTER TABLE command with the MODIFY clause on the EMP table.d.Use the ALTER TABLE command with the ADD clause on the EMP table.e.Use the ALTER TABLE command with the MODIFY clause on the EMP table.
Solution
d. Use the ALTER TABLE command with the ADD clause on the EMP table.
Here is a step-by-step guide on how to do it:
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First, ensure that the 'id' column in the DEPT table is a primary key. If it's not, you can set it as a primary key using the following command:
ALTER TABLE DEPT ADD PRIMARY KEY (id); -
Next, you can add a foreign key constraint on the 'dept_no' column in the EMP table that refers to the 'id' column in the DEPT table. Use the following command:
ALTER TABLE EMP ADD FOREIGN KEY (dept_no) REFERENCES DEPT(id); -
Run these commands in your SQL environment. If there are no errors, the foreign key constraint has been successfully added.
Remember, the data types of the 'dept_no' column in the EMP table and the 'id' column in the DEPT table must be the same. Also, there should not be any values in the 'dept_no' column of the EMP table that do not exist in the 'id' column of the DEPT table, otherwise, the foreign key constraint will fail.
Similar Questions
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Referential Integrity Constraint: Foreign Key
Drop the NOT NULL constraints from EMP table
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