order_date column.WHERE clause to filter out orders with invoice less than or equal to 20.order_id to get the number of unique orders for each month.customer_id to get the number of unique customers for each month.month, order_count, and customer_count.
erDiagram
Orders {
int order_id PK "Unique order identifier"
date order_date "Date when the order was placed"
int customer_id "Identifier of the customer who made the order"
int invoice "Total invoice amount for the order"
}