SQL Interview Question: What Happens When Adding a NOT NULL Column to a Large Existing Table? #sql

You have an existing table named employees containing 1 million records.

You execute the following SQL statement:

ALTER TABLE employees
ADD salary INT NOT NULL;

What will happen when this query is executed?

Will the query succeed or fail?
Why does this behavior occur?
How can this issue be resolved in a production environment with large datasets?

This question tests your understanding of:

ALTER TABLE behavior
NOT NULL constraints
Default values
Impact on large tables
SQL Server/MySQL/PostgreSQL schema modification concepts

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