Combining DISTINCT and ORDER BY for Unique Results
When faced with a dataset containing duplicate values, using DISTINCT to remove duplicates can be essential for obtaining unique results. However, when sorting is also required, using ORDER BY in the same SELECT statement can pose a challenge.
To address this issue, consider the following query:
SELECT Category FROM MonitoringJob ORDER BY CreationDate DESC
This query retrieves data from the MonitoringJob table, ordering the results in descending order by the CreationDate column. The desired outcome is a list of unique categories, sorted by the latest creation date. However, the query produces duplicate values.
One attempt to resolve this issue might be using DISTINCT:
SELECT DISTINCT Category FROM MonitoringJob ORDER BY CreationDate DESC
Unfortunately, this query fails because DISTINCT does not work with ORDER BY in a single statement.
To resolve this issue, an aggregate function and GROUP BY clause can be used:
SELECT DISTINCT Category, MAX(CreationDate) FROM MonitoringJob GROUP BY Category ORDER BY MAX(CreationDate) DESC, Category
This query:
This approach combines the power of DISTINCT to eliminate duplicates with the functionality of ORDER BY to sort the data, giving you unique results sorted in the desired order.
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