Answer for Remove Column record does not work with Change Statement

https://365datascience.com/dwqa-answer/answer-for-remove-column-record-does-not-work-with-change-statement/ -

Hi Jo!

Thanks for reaching out.

This is a very interesting question!

Basically, this modification doesn’t turn the dept_no into a Unique Key. Instead, it adds NULL as a default value. Moreover, it doesn’t affect the records that have been inserted so far in the table.

That’s why if you executed again the following query, for instance:

INSERT INTO departments_dup
(
dept_no,
dept_name
)
SELECT
*
FROM
departments;

you’ll manage to insert all for records with all department numbers available. However, if you only try to insert a record containing a value for the department name, then the value in the dept_no field will be null.

INSERT INTO departments_dup (dept_name) VALUES (‘Finance’);


Hope this helps.
Best,
Martin

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