MySQL LAST_VALUE

The MySQL LAST_VALUE window function is used to retrieve the value of an expression from the last row within a specified window frame. The window frame is a group of rows that are considered together for calculations. The LAST_VALUE function is particularly useful for analyzing trends and identifying patterns in data.

Syntax

The general syntax of the LAST_VALUE function is as follows:

LAST_VALUE(expression) OVER ([PARTITION BY partition_clause] ORDER BY order_clause [ROWS window_frame] | [RANGE window_frame])

Where:

expression is the expression whose last value is being calculated.
partition_clause is an optional clause that partitions the window frame into groups.
order_clause is an optional clause that orders the rows within the window frame.
window_frame is a clause that defines the range of rows in the window frame. It can be specified using the ROWS or RANGE clauses.

Example

Here’s a simple example:

CREATE TABLE example_table (
  id INT,
  category VARCHAR(255),
  value INT
);

INSERT INTO example_table VALUES
  (1, 'A', 10),
  (2, 'A', 20),
  (3, 'B', 30),
  (4, 'B', 40);

SELECT
  id,
  category,
  value,
  LAST_VALUE(value) OVER (PARTITION BY category ORDER BY id) AS last_value_within_category
FROM
  example_table;

This query selects the id, category, and value columns from the example_table and includes an additional column, last_value_within_category, which represents the last value of the value column within each category partition.

Conclusion

The MySQL LAST_VALUE function is a versatile tool for analyzing data within a window frame. It can be used to calculate various values, such as the last amount, the last time, or the last position. By using the PARTITION BY, ORDER BY, and ROWS or RANGE clauses, you can carefully define the scope of the window frame and obtain meaningful insights from your data.