Add a unique key

sql

ALTER TABLE users ADD CONSTRAINT uq_users_email UNIQUE (email);

Explanation

Unique constraints are commonly used for logins, slugs, and external identifiers.

Learn the surrounding workflow

Compare similar commands or jump into common fixes when this command is part of a bigger troubleshooting path.

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Use multiple columns as the logical primary key.

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Delete an entire schema and all objects inside it.

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Create a schema if it does not already exist.

Create a table with an auto-increment primary key and timestamps.