sql / beginner
Snippet
Ensuring Record Uniqueness with PRIMARY KEY Constraints
A PRIMARY KEY uniquely identifies each record in a database table. It ensures that duplicate identifiers cannot be inserted and that primary key values are never NULL.
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CREATE TABLE employees (employee_id INTEGER PRIMARY KEY,first_name VARCHAR(50),last_name VARCHAR(50));
Breakdown
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CREATE TABLE employees (
Initiates the creation of a new table named 'employees'.
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employee_id INTEGER PRIMARY KEY,
Defines 'employee_id' as an integer and sets it as the unique primary key for table rows.
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first_name VARCHAR(50),
Creates a column named 'first_name' holding text up to 50 characters.
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last_name VARCHAR(50)
Creates a column named 'last_name' holding text up to 50 characters.
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);
Closes the table definition statement.