Query Without Duplicate Rows

By Tiationg Kho |
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Query Without Duplicate Rows

SELECT DISTINCT col_name
FROM table_name;

SELECT DISTINCT column1, column2, column3
FROM table_name;

SELECT COUNT(DISTINCT col_name)
FROM table_name;
  • DISTINCT
    • Only get the unique values
    • Can be used with multiple columns
  • COUNT(DISTINCT col)
    • Counts all unique non-null values in the specified column

1141. User Activity for the Past 30 Days I

/* Write your T-SQL query statement below */

SELECT activity_date AS [day], COUNT(DISTINCT user_id) AS active_users
FROM Activity
WHERE activity_date > '2019-06-27' AND activity_date <= '2019-07-27'
GROUP BY activity_date;

1148. Article Views I

/* Write your T-SQL query statement below */

SELECT DISTINCT author_id AS id
FROM Views
WHERE author_id = viewer_id
ORDER BY author_id ASC;