Consider the following table with rows as an example:
Table Name: Products ProductId Price --------------- 1 10 1 10 2 20 3 30 3 30
Here assume that productId column should be unique after deleting. Now we see how to delete the duplicate records from the products table in different ways.
1. Using Rowid
The following Delete statement deletes the rows using the Rowid.
Syntax: Delete from <tablename> where rowid not in (select max(rowid) from <tablename> group by <unique columns or primary key>); Example: Delete from products where rowid not in (select max(rowid) from products group by productid);
2. Using temp table and Distinct
Here, first create a temp table and insert distinct rows in the temp table. Then truncate the main table and insert records from the temp table.
Create temporary table products_temp As Select Distinct ProductID, Price From Products; Truncate table Products; Insert into products Select * From products_temp;
3. Using temp table and Row Number analytic function.
The row_number analytic function is used to rank the rows. Here we use the row_number function to rank the rows for each group of productId and then select only record from the group.
Create temporary table products_temp As Select productid, price From ( Select productid, price, row_number() over (partition by productId order by price) group_rank From products ) Where group_rank = 1;