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Optimize your SQL queries to select unique records between two dates, ensuring you get the latest entry for each plate on the same day with our comprehensive guide.
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Selecting Unique Records Between Two Dates Based on Plates in SQL

In the world of database management, efficiently querying data can become quite a challenge—especially when you want to filter records based on specific criteria. One common scenario you might encounter is the need to select all records between two dates, while ensuring that you only select the latest record for each unique plate on the same day. In this post, we'll explore how to achieve that using SQL Server's capabilities, particularly the ROW_NUMBER() window function.

Understanding the Problem

Let's say you have a dataset containing entries related to various vehicles, including their details such as plate numbers, vehicle IDs, transaction types, and transaction dates. Your objective is to retrieve records that meet the following criteria:

Select all records between two specific dates.

If multiple records exist for the same plate on the same day, you wish to select only the most recent one, potentially using the BelgeID (document ID) as the determining factor.

The Challenge

Perform a selection based on a date range while ensuring unique entries for the same plate each day.

Sort records effectively and avoid duplications.

The SQL Solution

To solve this problem, we can leverage Common Table Expressions (CTEs) and the ROW_NUMBER() window function. Here's a step-by-step breakdown of the solution:

Step 1: Create a CTE

First, we'll enclose the existing SQL query in a Common Table Expression (CTE). This creates a temporary result set that we can use to partition and order our data.

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Step 2: Use ROW_NUMBER() Function

Next, we apply the ROW_NUMBER() function to assign a unique sequential integer to rows within a partition of a result set. We partition by Tarih (date) and Plaka (plate), ordering by BelgeID in descending order to ensure we get the latest entry first.

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Step 3: Filter for Unique Records

Finally, we select records only where rn (the row number) equals 1. This way, for each day and each unique plate, we only get the latest record.

Complete Query

Combining all the parts, here’s how the final SQL query looks:

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Conclusion

By employing a CTE and the ROW_NUMBER() window function, we can efficiently select unique records between two dates while ensuring that we pull the latest entry for each plate on the same day. This approach not only simplifies our query but also enhances performance when dealing with large datasets.

Now, you can confidently manage records in your SQL Server database while meeting complex selection criteria!