Ways of Identifying duplicate rows in SQL

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To find duplicate rows using partition and rank, you can use the following steps:

- First, you need to use the PARTITION BY clause to divide the rows in your table into groups based on one or more columns that you want to compare for duplicates. For example, if you want to find duplicate rows based on the name and address columns, you can use PARTITION BY name, address.

- Next, you need to use the ORDER BY clause to specify the order of rows within each partition. You can use any column that you want to sort by, such as the ID column. For example, you can use ORDER BY ID.

- Then, you need to use the RANK () function to assign a rank to each row within each partition. The rank starts from 1 and increases by 1 for each row. If two or more rows have the same values in the partition columns, they will have the same rank. For example, you can use RANK () OVER (PARTITION BY name, address ORDER BY ID) AS rank.

- Finally, you need to select the rows that have a rank greater than 1. These are the duplicate rows that have the same values in the partition columns as another row. You can use a subquery or a common table expression (CTE) to filter these rows. For example, you can use:

```sql
-- Using a subquery

SELECT * FROM (
  SELECT *, RANK () OVER (PARTITION BY name, address ORDER BY ID) AS rank
  FROM table_name
) t
WHERE rank > 1;

-- Using a CTE

WITH cte AS (
  SELECT *, RANK () OVER (PARTITION BY name, address ORDER BY ID) AS rank
  FROM table_name
)

SELECT * FROM cte WHERE rank > 1;

```

There are some other ways to find duplicate rows in SQL, depending on the database system and the requirements. Here are some examples:

- You can use the EXISTS or NOT EXISTS operator to check if a row exists in a subquery that matches the values of another row. For example, you can use this query to find duplicate rows based on the name and address columns:

```sql
SELECT * FROM table_name t1 
WHERE EXISTS (
  SELECT 1 FROM table_name t2
  WHERE t1.name = t2.name
  	AND t1.address = t2.address
  	AND t1.id <> t2.id
);

```

- You can use the JOIN clause to join a table with itself and compare the values of the columns. For example, you can use this query to find duplicate rows based on the name and address columns:


```sql
SELECT t1.* FROM table_name t1
JOIN table_name t2
	ON t1.name = t2.name
	AND t1.address = t2.address
	AND t1.id <> t2.id;
```

- You can use the DISTINCT or GROUP BY clause to select only the unique values of the columns and then use the EXCEPT or MINUS operator to subtract them from the original table. For example, you can use this query to find duplicate rows based on the name and address columns:

```sql
SELECT name, address FROM table_name

EXCEPT

SELECT DISTINCT name, address FROM table_name;
```

To identify duplicate rows using group by in SQL, you can use the following steps:

- First, you need to select the columns that you want to check for duplicates using the SELECT statement. For example, if you want to find duplicate rows based on the name and address columns, you can use SELECT name, address.
- Next, you need to use the GROUP BY clause to group the rows by the selected columns. For example, you can use GROUP BY name, address.
- Then, you need to use the COUNT function in the HAVING clause to filter the groups that have more than one row. These are the groups that contain duplicates. For example, you can use HAVING COUNT (*) > 1.
- Finally, you need to execute the query and see the results. For example, the complete query would look like this:

```sql
SELECT name, address FROM table_name 
	GROUP BY name, address 
	HAVING COUNT (*) > 1;
```

This query will return all the rows that have duplicate values in the name and address columns.