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SQL for beginners

Enforcing uniqueness with PRIMARY KEY #

A PRIMARY KEY marks a column as the unique identifier for each row in a table. No two rows can ever share the same primary key value, and the database will reject any attempt to insert a duplicate one.

CREATE TABLE table_name (
    id PRIMARY KEY,
    column_2,
    column_3
);
  • id PRIMARY KEY: Marks the id column as the table's primary key.

Every table you design should have a primary key. It is what lets you (and other tables, through foreign keys, which you will learn about next) reliably refer to one exact row.

Exercise #

Write a command that creates a table called reviews with the columns id, product_id, rating, and comment, where id is the primary key.

Tests #

  • The reviews table has the columns id, product_id, rating, and comment.
  • The id column is set as the primary key.
Solution 
CREATE TABLE reviews (
    id PRIMARY KEY,
    product_id,
    rating,
    comment
);
Output will be displayed here