<h2>Retrieve Rows with Maximum Value for a Column Based on Each Distinct Value in Another Column</h2>
<p>When working with large datasets, it is often necessary to retrieve specific rows based on certain criteria. One common scenario is needing to retrieve the maximum value for a particular column, but only for each distinct value in another column. This can be achieved using SQL queries and can be particularly useful in data analysis and reporting. In this article, we will discuss how to retrieve rows with maximum value for a column based on each distinct value in another column.</p>
<h3>Understanding the Problem</h3>
<p>Before we dive into the solution, let's first understand the problem at hand. Imagine you have a table with information about sales data for a company. The table has columns for <code>product_name</code>, <code>sales_date</code>, and <code>sales_amount</code>. You want to retrieve the highest sales amount for each distinct product in the table. This means that for each unique product, you want to retrieve the row with the highest sales amount.</p>
<p>To better visualize the problem, let's take a look at a sample table:</p>
<table>
<tr>
<th>product_name</th>
<th>sales_date</th>
<th>sales_amount</th>
</tr>
<tr>
<td>Product A</td>
<td>2021-01-01</td>
<td>1000</td>
</tr>
<tr>
<td>Product A</td>
<td>2021-01-02</td>
<td>1500</td>
</tr>
<tr>
<td>Product B</td>
<td>2021-01-03</td>
<td>2000</td>
</tr>
<tr>
<td>Product C</td>
<td>2021-01-04</td>
<td>3000</td>
</tr>
<tr>
<td>Product C</td>
<td>2021-01-05</td>
<td>3500</td>
</tr>
</table>
<p>In this example, we want to retrieve the rows with the maximum sales amount for each distinct product. This means we would want to retrieve the rows for Product A with a sales amount of 1500, Product B with a sales amount of 2000, and Product C with a sales amount of 3500.</p>
<h3>The Solution</h3>
<p>To solve this problem, we can use a combination of SQL functions and clauses. First, we will use the <code>MAX()</code> function to retrieve the highest sales amount for each product. Then, we will use the <code>GROUP BY</code> clause to group the results by product. This will give us the maximum sales amount for each distinct product.</p>
<p>The final query would look something like this:</p>
<code>SELECT product_name, MAX(sales_amount) AS max_sales_amount
FROM sales_data
GROUP BY product_name;</code>
<p>This query will return the following results:</p>
<table>
<tr>
<th>product_name</th>
<th>max_sales_amount</th>
</tr>
<tr>
<td>Product A</td>
<td>1500</td>
</tr>
<tr>
<td>Product B</td>
<td>2000</td>
</tr>
<tr>
<td>Product C</td>
<td>3500</td>
</tr>
</table>
<p>Now, to retrieve the entire row for each maximum sales amount, we can use this query as a subquery and join it back to the original table. This will give us the rows with the maximum sales amount for each distinct product.</p>
<p>The final query would look like this:</p>
<code>SELECT sd.product_name, sd.sales_date, sd.sales_amount
FROM sales_data sd
INNER JOIN (
SELECT product_name, MAX(sales_amount) AS max_sales_amount
FROM sales_data
GROUP BY product_name
) m ON sd.product_name = m.product_name AND sd.sales_amount = m.max_sales_amount;</code>
