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SQL for beginners

Selecting unique values with DISTINCT #

A table often has repeated values in a column. The DISTINCT keyword removes duplicate rows from the result, keeping only unique values:

SELECT DISTINCT
    column_name
FROM
    table;

For example, our customers table has a gender column that only ever contains M or F. Instead of getting the value once per customer, DISTINCT gives us each unique value once:

SELECT DISTINCT
    gender
FROM
    customers;

DISTINCT applies to the whole row being selected, so if you select multiple columns, only rows where all selected columns match together are treated as duplicates.

Exercise #

We have already created a table products with the columns id, name, category, and price. Write a command that retrieves the distinct list of category values from products.

Tests #

  • The result has a category column.
  • The result contains each category value exactly once, with no duplicates.
Solution 
SELECT DISTINCT
    category
FROM
    products;
Output will be displayed here