What is a primary key?
A primary key is the column that uniquely identifies each row in a table, like an ID number nobody else can have.
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A primary key is one column (or a small set of columns) whose value is different for every row and never empty. It is the national ID number of a table row: two people may share a name, but not an ID. The database enforces this rule and builds an index on it automatically, so finding a row by its key is instant.
Most tables use an auto-incrementing integer called id or a random UUID. Natural values like email addresses can work but change over time, so a surrogate key is safer. Other tables refer to this key through foreign keys, which is how a relational database links orders to customers or comments to posts.
CREATE TABLE customers (
id SERIAL PRIMARY KEY,
email TEXT UNIQUE NOT NULL
);See also: What is a foreign key? and What is an index (database)?
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See also
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Repos in the wild
- DuckDB duckdb/duckdb An in-process analytical SQL database. Run fast SQL directly on CSV, Parquet and JSON files, from the command line or inside Python and other languages. GitHub
- SQLite (official Git mirror) sqlite/sqlite The source tree of SQLite, the self-contained SQL database engine embedded in phones, browsers and countless applications, mirrored to GitHub by its developers. GitHub
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