In this post we look at ways to remove all duplicate rows except one in an SQL database. For all examples in this article, we'll be using the following MySQL "user" table: +---+---+|id|name|+---+---+|1|john||2|david||3|john||4|john||5|wayne||6|david|+---+---+...
The ROWIDs are then returned to the DELETE statement at the top, which only deletes records where the ROW_NUMBER function (which has an alias of “dup” in this example) are greater than one. (The AskTOM thread uses “WHERE dup <> 1” but it achieves the same thing). It’s a goo...
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This returns you a single row for each combination. This includes the rows without duplicates. To return just the copied values you need to filter the results. This is those where the count is greater than one. You can do this with a having clause, like so: Copy code snippet Copied to ...
If we look at the result set, we can easily understand thatBookNumber: 3andBookNumber: 4are duplicate rows. Previously, it was explained in detailhow to remove duplicates in SQL. We must delete them to keep the database consistent.
Duplicate rows could be remove or drop from Spark SQL DataFrame using distinct() and dropDuplicates() functions, distinct() can be used to remove rows
-- Now delete the duplicate records WITH CTE(id,name,age,Duplicates) AS ( SELECT id,name,age, ROW_NUMBER() OVER (PARTITION BY id, name, age ORDER BY id) AS Duplicates FROM Test ) DELETE FROM CTE WHERE Duplicates > 1 GO Now check the table to make sure duplicates are being removed...
To delete similar records, i.e. where the records are not the same but one field is the same and only one copy needs to be preserved, try the following SQL: delete T1 from MyTable T1, MyTable T2 where T1.dupField = T2.dupField ...
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Before you begin, start the MySQL prompt and open the database in question with the command below: USE [database];Copy For example, to use thetestdatadatabase, type the following: USE testdata;Copy Option 1: Remove Duplicate Rows Using the ROW_NUMBER() Function ...