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:

<code class="language-sql">SELECT group, MAX(date), checks
FROM table
WHERE checks > 0
GROUP BY group
ORDER BY group DESC</code>

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:

<code class="language-sql">SELECT group, MAX(date) AS max_date
FROM table
WHERE checks > 0
GROUP BY group</code>

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:

<code class="language-sql">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;</code>

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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