sql / intermediate
Snippet
Enforcing Uniqueness with Constraints
A UNIQUE constraint ensures that all values in a column are different across all rows. Unlike a PRIMARY KEY, a table can have multiple UNIQUE constraints, and they allow for data integrity and automatic index creation.
snippet.sql
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CREATE TABLE user_accounts (user_id INTEGER PRIMARY KEY,email_address VARCHAR(255) UNIQUE,username VARCHAR(50) NOT NULL);
Breakdown
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user_id INTEGER PRIMARY KEY
Defines a unique identifier for the row that also cannot be null.
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email_address VARCHAR(255) UNIQUE
Specifies that no two users can share the same email address.
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username VARCHAR(50) NOT NULL
Ensures that the username field must always contain a value.