What are the different types of constraints in PostgreSQL?
An example of an AI chatbot conversation about PostgreSQL constraints and their types.
What are the different types of constraints in PostgreSQL?
In PostgreSQL, constraints are rules that enforce data integrity. The main types include NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK.
Can you explain the difference between PRIMARY KEY and UNIQUE constraints?
Sure! A PRIMARY KEY constraint uniquely identifies each row in a table and cannot accept NULL values, while a UNIQUE constraint also ensures uniqueness but can accept one NULL value.
What happens if I try to insert a duplicate value in a column with a UNIQUE constraint?
If you attempt to insert a duplicate value in a column with a UNIQUE constraint, PostgreSQL will raise an error and prevent the insertion.
How do I add a CHECK constraint to an existing table?
You can add a CHECK constraint using the ALTER TABLE command. For example: ALTER TABLE table_name ADD CONSTRAINT constraint_name CHECK (condition);.
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