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SQL-for-Data-Analytics-Third-Edition

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Question about the solution for activity 5.01

This issue concerns the calculation of deciles in the solution code.

SQL-for-Data-Analytics-Third-Edition/Chapter05/Activity5.01/Activity5.01.sql

Line 39 in 78f7929

-- Question 4

The book presents the following question in activity 5.01:

4. Calculate which decile each date would fall into compared to other days based on their daily 30-day rolling sales amount.

Problem:
Line 68 of the solution code uses the window function NTILE(10) OVER (ORDER BY moving_avg DESC) AS decile to calculate the decile for each value group in the moving_avg column. However, the resulting decile column appears to be identical to what would be obtained using NTILE(10) OVER () AS decile, which omits the ORDER BY clause.