This tutorial step by step shows you how to delete duplicate rows from a table in SQL Server. , `name`), while removing all other duplicates. In this article, I would like to share the best way to delete duplicate rows in SQL server from a table. Aug 28, 2024 · Learn how to delete duplicate rows in SQL with practical methods and examples to clean up your database efficiently. In other words, it de-dupes the table. I have a table that has a lot of duplicates in the Name column. 300,000+ rows). 4 This is not a query but a delete statement. May 27, 2024 · How to Delete duplicate rows in SQL using CTE While procedures are a great way to encapsulate logic, removing duplicates with CTEs is typically done within a single SQL statement. In this article, we will learn how to find and delete duplicate values from a table in SQL Server. This blog covers frequently asked SQL interview problems, explained step-by-step with: clear intent correct SQL beginner-friendly explanations advanced variations for experienced candidates Feb 16, 2022 · There are many ways to get or identify the duplicate rows and delete duplicate rows, we have to consider if the given table has unique index or not. Deleting duplicate rows in a database table is a common task in SQL, and it’s important for maintaining data integrity. for example, my Feb 11, 2009 · Tables with no primary key When you have duplicates in a table that has no primary key defined, and you are using an older version of SQL Server, such as SQL Server 2000, you do not have an easy way to identify a single row. Possible Duplicate: Duplicate result Interview - Detect/remove duplicate entries I have a SQL Query, which returns a table with one column. The duplicate value comes from one Feb 11, 2009 · Tables with no primary key When you have duplicates in a table that has no primary key defined, and you are using an older version of SQL Server, such as SQL Server 2000, you do not have an easy way to identify a single row. The Problem - Removing Duplicates in SQL Let’s say you have a table with some data in it. 5 days ago · While the ability to drop all constraints on a table in SQL Server is a powerful tool, it must be used with extreme caution and thorough planning. I have duplicate rows in my table and I want to delete duplicates in the most efficient way since the table is big. The best method to use depends on the specific situations like the number of duplicate rows, the size of the table, the performance of the MySQL server and the desired results. SQL remove duplicates Removing duplicates from a SQL database is a common task that can help improve data quality and query performance. May 20, 2019 · How to delete duplicate records in SQL? [duplicate] Asked 6 years, 7 months ago Modified 6 years, 7 months ago Viewed 14k times Jul 28, 2019 · This selects/deletes all duplicate records except one record from each group of duplicates. There are over 3481 records returned by the first query to do this one by one manually. So, the delete leaves all unique records + one record from each group of the duplicates. How can I find the duplicate rows like the first query and delete all but the most recent like the second? May 30, 2023 · Find duplicate rows Before I show you how to delete the duplicates, let us first write a query to find the duplicate rows. sql sql-server t-sql join duplicates edited May 14, 2015 at 18:37 HaveNoDisplayName 8,537 106 41 50 pyspark. In this article, we will explore some of the most effectiv 1 day ago · I’m explicit about the a. DataFrame. For deleting such rows, we need to use the DELETE keyword along with self-joining the table with itself. Dec 6, 2023 · Fortunately most SQL databases provide us with an easy way to remove duplicates. How I can removed all duplicate combinations from SQL table? Dec 7, 2024 · In this tutorial, we'll look at four different ways to delete duplicate records from a table in SQL Server. We cover almost every SQL 14 hours ago · Feature Duplicates UNION Removes duplicates UNION ALL Keeps all rows, including duplicates Performance Slower (because of sorting) Faster (no de-duplication) Use case When you want distinct rows When duplicates are meaningful Example: SELECT city FROM customers UNION SELECT city FROM vendors; →Returns a unique list of cities. There are a few different ways as we discussed above to delete duplicate rows from MySQL tables. How to delete duplicate rows based on one column in SQL? To delete duplicates based on one column, use a self-join on the table and delete the rows where the EMPLOYEE_ID is greater than the matching duplicate record. Here’s a guide on how to delete duplicate rows in SQL: Jan 10, 2025 · This article provides a script that you can use to remove duplicate rows from a SQL Server table. pyspark. This guide explains how to delete duplicate rows from a table in SQL Server. To define a key on the table, we have to delete the duplicate rows from the table. Jan 10, 2025 · This article provides a script that you can use to remove duplicate rows from a SQL Server table. Nov 28, 2025 · A frequent scenario is needing to **retain only one row per value in a specific column** (e. Duplicate records in a table can occur for various reasons, such as user errors, system integration problems, data migration problems, etc. Feb 17, 2022 · Hi, I am new to Proc SQL, I would like to know how we can remove the duplicates from dataset and achieve the exactly same thing that I can achieve through the PROC SORT. Fortunately, there are several ways to remove duplicate data in SQL. To do this, we’ll use the ROW_NUMBER () function to help find duplicates with name and ages. productid constraint to avoid duplicates. This is one of the efficient methods to delete records and I would suggest using this if you have SQL Server 2005 or 2008. Jul 23, 2025 · Through this article, we will learn how to delete duplicate columns from a database table. The setting has to be adjusted before any temp buffer is used in your current session. However, when working with a poorly designed database or unclean data, you may need to find duplicates yourself and delete them manually. Jul 30, 2024 · In this tutorial, we’ll learn how to find duplicate rows in our SQL tables and remove them correctly. The Group By clause groups data as per the defined columns and we can use the COUNT function to check the occurrence of a row. The rows, of course, will not be perfect duplicates because of the existence of the RowID identity field. A table may contain duplicate rows if the key not defined. Dec 18, 2018 · This article discusses two different approaches available to remove duplicate rows from SQL table(s) which often becomes difficult over time as data grows if this is not done on time. By using dynamic SQL scripts and understanding the dependency hierarchy, you can manage even the most complex schema changes with confidence. SQL DELETE DUPLICATE ROWS When dealing with large datasets, it's common to encounter duplicate records in a table. Additionally, we will include a detailed example, syntax, and FAQs for better understanding. Create a Sample Jul 23, 2025 · Using SQL to manage duplicate rows ensures that our database remains optimized and consistent. Delete duplicate columns in SQL Asked 11 years, 5 months ago Modified 6 years, 9 months ago Viewed 18k times I don't think your snippet (using HAVING) which identifies rows to be deleted works; it will delete all the rows which have duplicates, whereas I think the requirement is to keep one. The simplest way to use this is with the DISTINCT keyword at the start of the SELECT list. I am trying with sql but having diffi Dec 30, 2024 · One common task in SQL is finding and deleting duplicate records. Duplicate rows can occur for various reasons, such as data entry errors or system glitches. Example: First, we will create a demo SQL database and table, on which we will use the Delete Duplicate Rows command. Use ROW_NUMBER, CTE and DELETE techniques to clean up your database and improve performance. Dec 30, 2024 · One common task in SQL is finding and deleting duplicate records. Therefore, you cannot simply delete this row by specifying a WHERE clause in a DELETE statement. Jan 13, 2026 · SQL interviews are not about memorizing syntax — they test data thinking, edge-case handling, and real-world querying skills. In SQL Server, your business key plays the role of that seat definition. Step-by-step instructions and practical tips with AI2sql for cleaner SQL data. Dec 12, 2020 · Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java, XML and more. DataFrame ¶ Return a new DataFrame with duplicate rows removed, optionally only considering certain columns. Discover how to write a SQL query to remove duplicate rows. What is a Duplicate Row? I know I can run the following query below to find "duplicate" rows based on multiple columns doing something like this: SELECT PosId, OrgId FROM PosOrg GROUP BY PosId, OrgId HAVING Feb 16, 2022 · There are many ways to get or identify the duplicate rows and delete duplicate rows, we have to consider if the given table has unique index or not. The DISTINCT Clause The most common way to remove duplicate rows from our query results is to use the DISTINCT clause. You can eliminate these duplicates using various SQL techniques and clauses. It will delete/remove duplicate rows from your table Jan 8, 2010 · This means keeping one record from the group and deleting all other similar/duplicate records. Jul 15, 2025 · To Delete Duplicate Rows in MS SQL Server, we will use the below method that helps us to perform delete duplicate rows from the table as defined below: Using GROUP BY and HAVING Clause I am not versed in SQL enough to figure out how to use the rows in the first query to delete the duplicates leaving behind the most recent. Nov 1, 2023 · Learn how to find and delete duplicate rows in SQL or completely delete records in SQL including Joins using different methods. Using common techniques like ROW_NUMBER() with PARTITION BY, you can identify and remove duplicate rows while keeping the original. Sample Data Suppose we have a table with the following data: SELECT * FROM Pets; Result: In this tutorial, you will learn how to delete duplicate rows in MySQL by using the DELETE JOIN statement or an immediate table. Dec 5, 2025 · Can be removed using SQL functions like ROW_NUMBER () or COUNT (). Mar 27, 2024 · PySpark distinct() transformation is used to drop/remove the duplicate rows (all columns) from DataFrame and dropDuplicates() is used to drop rows based Nov 28, 2021 · In SQL, some rows contain duplicate entries in multiple columns (>1). First, we’ll look at a database management system (DBMS) agnostic approach to find and remove duplicates. In my example I want achieve the output exactly looks like CLASS1 dataset using PROC SQL. Jul 23, 2025 · In this article, we will explain how to find duplicate records in SQL using effective methods like GROUP BY, HAVING, and subqueries. Sep 13, 2024 · Learn how to find and delete duplicate records in SQL using three effective methods: GROUP BY, subqueries, and Common Table Expressions (CTE). I want to remove duplicate combinations rows using MS SQL? Remove latest duplicate records from MS SQL FriendsData table. dropDuplicates # DataFrame. To make the operation fast you want to allocate enough temporary buffers for the session. It can be done by many ways in sql server the most simplest way to do so is: Insert the distinct rows from the duplicate rows table to new temporary table. Suppose we have a table like this: SELECT * FROM Dogs Learn different methods to remove duplicate rows from a SQL table using SQL Server. The following lists the duplicates, but I don't know how to delete the duplicates and just k Dec 28, 2022 · Database design best practices recommend using the UNIQUE constraint to prevent duplicates in a database. Create a Sample In this article, we will learn how to find and delete duplicate values from a table in SQL Server. This concise guide covers using GROUP BY and HAVING clauses to effectively identify and resolve duplicates. Mar 10, 2023 · Duplicates can be a big problem in SQL databases as they can slow down query performance and waste valuable storage space. So as a first step Optimiere deine Datenbank mit SQL-Lösungen zum Entfernen von Duplikaten. Check out the examples below to get real world examples on how to delete duplicate records from a table. Feb 1, 2024 · This tutorial shows you how to use various techniques: DELETE join, subquery, and immediate table to delete duplicate rows in PostgreSQL. For real systems, I also apply date filters so I’m only analyzing a recent window, such as the last 90 days. Removing duplicates rows from a SQL Server table with a unique index Test We would like to show you a description here but the site won’t allow us. Jul 23, 2025 · Conclusion Duplicate rows can be a problem in MySQL databases. You’ve found out that there is some duplicate data in this table. Jul 15, 2025 · To Delete Duplicate Rows in MS SQL Server, we will use the below method that helps us to perform delete duplicate rows from the table as defined below: Using GROUP BY and HAVING Clause May 30, 2023 · Find duplicate rows Before I show you how to delete the duplicates, let us first write a query to find the duplicate rows. e. here I attached image which highlights duplicate column combinations. SQL delete duplicate Rows using Group By and having clause In this method, we use the SQL GROUP BY clause to identify the duplicate rows. Let's explore the various techniques to achieve this efficiently. I'd like to only keep one row for each. It records inaccurate data and is also unable to fetch the correct data from the database. You can use withWatermark() to limit Nov 17, 2009 · This approach is only useful where there are lots of rows to delete from all over the table. After some research, I have come up with this query: WITH TempEmp AS ( SELECT na Sep 10, 2021 · Do you need to use SQL to remove duplicates in your tables? Learn how to write an SQL query to remove duplicate data in this article. So if you have two identical rows, it deletes one of them and keeps the other. dropDuplicates ¶ DataFrame. Then delete all the data from duplicate rows table then insert all data from temporary table which has no duplicates as shown below. 🔹 Key Learnings: Used a subquery with 3 days ago · In this guide, we explain 150+ SQL commands in simple words, covering everything from basic queries to advanced functions for 2026. I need to remove duplicate rows from a fairly large SQL Server table (i. Sep 10, 2025 · Learn how to delete duplicate records in SQL efficiently. dropDuplicates(subset=None) [source] # Return a new DataFrame with duplicate rows removed, optionally only considering certain columns. Dec 28, 2022 · Database design best practices recommend using the UNIQUE constraint to prevent duplicates in a database. Learn how to identify and remove duplicate rows in SQL using GROUP BY, HAVING, DELETE, and ROW_NUMBER functions. Dec 11, 2025 · Data sets tend to grow in ways that leave stray duplicates behind from imports, batch processes, or plain accidents. For a streaming DataFrame, it will keep all data across triggers as intermediate state to drop Delete duplicate rows in SQL Server effortlessly! Learn how to remove duplicate records from your database. 3️⃣ of #100OfLeetCode 🚀 Solved LeetCode 196: Delete Duplicate Emails A must-know SQL problem for understanding subqueries and data cleanup logic. The returned data may be duplicate. You can use withWatermark() to limit Sep 18, 2025 · Sometimes we required to remove duplicate rows from a table although table has a UniqueID Column with identity. May 19, 2023 · I made multiple inserts (by error) in a Delta table and I have now strict duplicates, I feel like it's impossible to delete them if you don't have a column "IDENTITY" to distinguish lines (the primary key is RLOC+LOAD_DATE): it sounds odd to me not to be able to do any anything after data definitio Jun 5, 2024 · Table of Contents Delete Duplicate Records in SQL Server Removing duplicate records is one of the most common administrative tasks for any database administrator or SQL Server developer. For just a few duplicates, use a plain DELETE. In most cases where you need to delete duplicates, you'd come with a criteria to either delete the most recent or the oldest and keep just the one original record. Mar 6, 2023 · Solution This solution to remove duplicates in SQL is similar to the solution for finding duplicate rows we showed earlier, but here we want to keep one of the rows and delete the rest. You can also automate the duplicate removal. Find easy, practical steps for SQL Server, MySQL, and PostgreSQL data cleanup. For a streaming DataFrame, it will keep all data across triggers as intermediate state to drop duplicates rows. productid < b. Sep 2, 2020 · Find duplicate values in SQL with ease. . dataframe. Duplicates occur when there are multiple rows in a table with identical values in one or more columns. Jul 20, 2021 · In this scenario, the ROW_NUMBER () function can be used with a common table expression (CTE) to sort the data then delete the subsequent duplicate records. Oct 29, 2024 · Streamline your database with SQL remove duplicates solutions. g. We would like to show you a description here but the site won’t allow us. To be more specific, it deletes duplicate rows but keeps one. Hier findest du einfache, praktische Schritte zur Bereinigung von SQL Server-, MySQL- und PostgreSQL-Daten. \n\n## Self Join and Modern SQL Tooling in 2026\nEven with AI-assisted query builders and SQL copilots, I still write self joins by hand. Sep 12, 2010 · I have a table which looks like that: As You see, there are some date duplicates, so how to select only one row for each date in that table? the column 'id_from_other_table' is from INNER JOIN wit Dec 7, 2024 · In this tutorial, we'll look at four different ways to delete duplicate records from a table in SQL Server. This blog will guide you through identifying duplicate rows and provide step-by-step methods to delete duplicates, ensuring only one row remains per `name` column. And you want to get rid of the duplicates. 1. You mentioned millions of rows. Delete duplicate columns in SQL Asked 11 years, 5 months ago Modified 6 years, 9 months ago Viewed 18k times How to Delete Duplicate Records from a Table in Oracle SQL Duplicate records are common in data due to data entry errors, improper joins, or integration issues. This guide covers the syntax and examples for different database systems. Read on to learn how to find duplicates in an SQL database and how to delete them. dropDuplicates(subset: Optional[List[str]] = None) → pyspark. In the table, we have a few duplicate records, and we need to remove them. Jan 25, 2022 · The following example uses T-SQL to delete duplicate rows in SQL Server. Suppose we have a table like this: SELECT * FROM Dogs Spot duplicate rows in your SQL data effortlessly! Identify and remove duplicate records with ease. Oracle provides multiple SQL techniques to detect and remove duplicates efficiently. Nov 17, 2009 · This approach is only useful where there are lots of rows to delete from all over the table. You can say a duplicate means “same seat number,” but if the stadium can sell the same seat for different dates, you actually need “ (EventDate, Section, Row, Seat)” to call something a duplicate. sql. The query below will find the count of records that have the same values. For a static batch DataFrame, it just drops duplicate rows. May 8, 2013 · I can't delete the row via a GUI (in this case MySQL Workbench, but I'm looking for a database agnostic approach) because it refuses to perform tasks on tables without primary keys (or at least a UQ NN column), and I cannot add a primary key, because there is a duplicate in the column that would become the key. See examples of using group by, having, max, cte, rank and row_number functions. As we know that duplicity in our database tends to be a waste of memory space.

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