Extracting Maximum Date Rows with Non-Zero Check Amounts in SQL
This example demonstrates how to select unique groups with the most recent dates and non-zero check values from a dataset containing groups, dates, and monetary values (cash and checks).
An initial attempt using this query proved insufficient:
SELECT group, MAX(date), checks FROM table WHERE checks > 0 GROUP BY group ORDER BY group DESC
This query returned all dates and check values for each group, not just the data from the row with the maximum date.
The solution involves a two-step approach:
First, we identify the maximum date for each group with non-zero check values:
SELECT group, MAX(date) AS max_date FROM table WHERE checks > 0 GROUP BY group
Then, we join this result set back to the original table to retrieve the corresponding checks
(and other relevant columns) for those maximum date rows:
SELECT t.group, a.max_date, t.checks FROM table t INNER JOIN ( SELECT group, MAX(date) AS max_date FROM table WHERE checks > 0 GROUP BY group ) a ON a.group = t.group AND a.max_date = t.date;
This inner join ensures only rows matching both the maximum date and non-zero check criteria are included in the final output.
Best Practice: Using descriptive and non-reserved words for column names (e.g., group_id
instead of group
) improves code readability and reduces the risk of errors.
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