Скачать или смотреть How to Add an Alphabet with Condition Value More Than One in PostgreSQL

Discover how to effectively add alphabets to your data in PostgreSQL, ensuring accurate condition checks for duplicate values. Explore a structured solution using SQL techniques.
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This video is based on the question https://stackoverflow.com/q/67364901/ asked by the user 'omik' ( https://stackoverflow.com/u/15240737/ ) and on the answer https://stackoverflow.com/a/67365005/ provided by the user 'Tim Biegeleisen' ( https://stackoverflow.com/u/1863229/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Add an Alphabet with Condition Value More Than One in PostgreSQL

Managing duplicate records in databases often requires clever solutions to ensure data integrity while maintaining readability. In this post, we will address a specific challenge that arises when working with PostgreSQL: how to append an alphabet at the end of a field (in this case, no_surat) when certain conditions are met. Specifically, we want to add an alphabet only when the same value appears more than once in the account field.

The Problem

A user faced the requirement of appending an alphabet to the no_surat field based on the condition that an account has multiple entries. For example, if an account like 337 has several values, the no_surat should be appended with an alphabet (A, B, C, etc.). However, if the account has only one value (like 335), the alphabet should not be added.

The initial SQL query attempted to implement this logic but failed to exclude accounts with only one entry. Thus, an additional alphabet was erroneously added to account 335.

Given Records

The user provided the following example records that illustrate the problem:

[[See Video to Reveal this Text or Code Snippet]]

In this dataset, note that account 335 should not have an appended alphabet since it has only one entry.

The Solution

To solve this problem correctly, we can use a Common Table Expression (CTE) to first identify the number of entries per account, and then format the no_surat accordingly. Below is the revised SQL query that accomplishes this:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Query

Common Table Expression (CTE):

The cte selects distinct records based on ADDRESS while simultaneously:

Counting records using COUNT(*) OVER (PARTITION BY ACCOUNT), which tells us how many entries each account has.

Assigning a row number to each entry with ROW_NUMBER() OVER (PARTITION BY ACCOUNT ORDER BY NO_SURAT DESC). This allows us to manage how we append the alphabet.

Final Selection with CASE:

The final SELECT statement checks the count (cnt):

If cnt is greater than 1, it appends the corresponding letter (determined by the row number) to the NO_SURAT.

If cnt is equal to 1, it simply returns the NO_SURAT without modification.

Conclusion

By using this structured approach, we ensure that alphabets are only appended to those no_surat fields where the corresponding account has more than one entry. This implementation not only solves the problem at hand but also ensures clarity and maintainability of your SQL queries.

Feel free to try this solution in your PostgreSQL database and tailor it to fit your dataset. Happy querying!