[Solved] Better tsql query to figure out who\'s a new customer (or alternative to NOT EXISTS)

How to optimize this SQL query?

In case you have your own slow SQL query, you can optimize it automatically here.

For the query above, the following recommendations will be helpful as part of the SQL tuning process.
You'll find 3 sections below:

  1. Description of the steps you can take to speed up the query.
  2. The optimal indexes for this query, which you can copy and create in your database.
  3. An automatically re-written query you can copy and execute in your database.
The optimization process and recommendations:
  1. Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.
Optimal indexes for this query:
CREATE INDEX order_idx_orderdate ON order (orderDate);
CREATE INDEX person_idx_id_company_id ON person (id,company_id);
CREATE INDEX person_idx_company_id_id ON person (company_id,id);
The optimized query:
        DISTINCT p1.company_id 
    order o JOIN
        person p1 
            ON (
                o.person_id = p1.id 
                AND p1.company_id IS NOT NULL
        o.orderDate > '2017-01-01' 
        AND o.orderDate < '2017-09-01' 
        AND NOT EXISTS (
            order o2 JOIN
                person p2 
                    ON (
                        o2.person_id = p2.id 
                        AND p2.company_id = p1.company_id
                o2.orderDate < '2017-01-01'

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* original question posted on StackOverflow here.