How to Efficiently Select Max Date Rows with Non-Zero Check Values in SQL?

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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