Unpivoting Data

The Problem

Data arrived in a "Wide" format with separate columns for each month. I needed it "Long" for analysis.

The Technique: UNION ALL

SELECT product, 'Jan' AS month, jan_sales AS amount FROM wide_table

UNION ALL

SELECT product, 'Feb' AS month, feb_sales AS amount FROM wide_table

UNION ALL

SELECT product, 'Mar' AS month, mar_sales AS amount FROM wide_table;

PostgreSQL: UNNEST or LATERAL

For cleaner unpivoting, use `LATERAL` with `VALUES`.

*Day 83: Dynamic SQL Basics.*