Recap - LEAD & LAG

Available tables and columns:

• air_conditioners: id, efficiency, strength, month

We want to track how air conditioner performance changes over time. Your task is to find air conditioners that had declining performance between months.

Here's what to do:

1. For each air conditioner in each month, calculate its performance ratio by dividing the average efficiency by the average strength using AVG(efficiency)/AVG(strength), grouped by id and month
2. Compare each air conditioner's current month performance with its performance two months later
3. Find cases where the current performance is more than half of the future performance (current ratio ÷ future ratio > 0.5)
4. Return the air conditioner id, the month, and the comparison ratio named ratio_two_months for these cases