In this blog post, we will explore how to use the SQL LAST_VALUE function with the MERGE statement. The LAST_VALUE function is a powerful analytical function that allows us to retrieve the last value in a set of rows based on a specified criteria. The MERGE statement is used to perform both INSERT and UPDATE operations in a single query.

What is the LAST_VALUE Function?

The LAST_VALUE function is used to retrieve the last value in a set of rows based on the specified criteria. It can be used to find the last record in a group, the last record in a partition, or the last record overall in the result set. The LAST_VALUE function is commonly used in conjunction with the OVER clause to define the partition or order by criteria.

What is the MERGE Statement?

The MERGE statement is a powerful SQL construct that allows you to perform both INSERT and UPDATE operations in a single query. It combines the functionality of the INSERT and UPDATE statements, making it efficient for handling large sets of data. The MERGE statement uses a source table to match and update records in a target table based on a specified condition.

Using LAST_VALUE with MERGE

To demonstrate how to use the LAST_VALUE function with the MERGE statement, let’s consider a scenario where we have two tables: source_table and target_table. We want to update the target_table with the last value from the source_table for each corresponding record.

Here’s an example of how the SQL code would look like:

MERGE INTO target_table t
USING (
  SELECT id, 
         value,
         LAST_VALUE(value) OVER (PARTITION BY id ORDER BY date_col) AS last_value
  FROM source_table
) s
ON (t.id = s.id)
WHEN MATCHED THEN UPDATE SET
  t.last_value = s.last_value
WHEN NOT MATCHED THEN INSERT VALUES
  (s.id, s.last_value);

In the above example, we start by selecting the id, value, and the LAST_VALUE from the source_table using the OVER clause, partitioning by id and ordering by date_col. We then use this derived table s as the source for our MERGE statement.

The MERGE statement matches records based on the id column and performs an UPDATE to set the last_value in the target_table when a match is found. If no match is found, it performs an INSERT to create a new record with the appropriate values.

Conclusion

In this blog post, we explored how to use the SQL LAST_VALUE function with the MERGE statement. The combination of these two features allows you to efficiently update a target table with the last value from a source table. By leveraging the power of SQL, you can simplify your data manipulation tasks and improve the performance of your queries.

#SQL #LAST_VALUE #MERGE