Question

Requests can be made for multiple items and the only key is the surrogate request_id

I have the following query which returns a result set of 9 digit phone numbers

SELECT phone_number FROM purchases
WHERE item_type = 'popcorn'
GROUP BY phone_number;

I would like to then retrieve a list of of every DISTINCT item_type requested by each of those phone_number that was not ‘popcorn’ and then GROUP BY that item_type. IE I want to know what similar products customers tend to buy.

The desired result set may look something like this

item        COUNT(*)
pretzels    200
chips       150
crackers    125
…           …

In this case the number of phone_number‘s who bought popcorn and pretzels was 200 (I’m interested in this value). The total number of purchase of pretzels by people who bought popcorn was 1,000 but this is not the value I am interested in.

How can I create a single query that only specifies the item_type and retrieves a result like the above which shows items customers also bought?

Also – If someone can help me make a more descript title that would be appreciated.

EDIT

Here is the table

CREATE TABLE purchases(
    request_id BIGINT NOT NULL auto_increment,
    phone_number INT(9) NOT NULL,
    item_type VARCHAR(256) NOT NULL,
    PRIMARY KEY(request_id)
);

EDIT

Request for desired output based on this data http://www.sqlfiddle.com/#!2/23236/2

item        COUNT(*)
cc          1
notpopcorn  1

Answer 1

I would like to then retrieve a list of of every DISTINCT item_type
requested by each of those phone_number that was not ‘popcorn’ and
then GROUP BY that item_type. IE I want to know what similar products
customers tend to buy.

Try this:

SELECT item_type as item, COUNT(*)
FROM purchases 
WHERE phone_number NOT IN (SELECT DISTINCT phone_number 
                           FROM purchases
                           WHERE item_type = 'popcorn')
GROUP BY item_type;

SQL Fiddle Demo

Update: Try this:

SELECT item_type as item, COUNT(*)
FROM purchases 
GROUP BY item_type, phone_number
HAVING phone_number IN (SELECT DISTINCT phone_number 
                           FROM purchases
                           WHERE item_type = 'popcorn')
  AND item_type <> 'popcorn';

Updated SQL Fiddle Demo