Added INTERPOLATE Extension to ORDER BY with FILL

Why it matters

The INTERPOLATE extension enhances the WITH FILL feature by enabling users to generate intermediate rows with interpolated values when filling gaps in ordered query results. This solves the problem of missing data points in time series or ordered datasets, providing smoother and more meaningful data interpolation for analysis and reporting.

How to use it

Use the WITH FILL INTERPOLATE syntax alongside the ORDER BY clause in your SELECT queries. This instructs ClickHouse to fill missing values with interpolated data instead of gaps or default fill values. For example:

SELECT
    timestamp,
    value
FROM
    my_table
ORDER BY
    timestamp WITH FILL INTERPOLATE

This will fill missing timestamps and compute intermediate value fields via interpolation.