Question

I have two examples of tables I am using
I am using the output to build arrays so my output needs to be a single column

First table is a list of products

    PRODUCT ID    PRODUCT_NAME
    01            product1
    02            product2
    03            product3
    04            product4
    05            product5
    06            product6
    07            product7
    08            product8
    09            product9
    10            product10
    11            product11
    12            product12

Table two is a list of purchases

    SALESID       PRODUCT_NAME       USERID       DATE
    01            product1           001ABC       11-10-2012
    02            product5           001ABC       11-11-2012
    03            product1           002XYZ       11-11-2012
    04            product12          001ABC       11-13-2012
    05            product7           001ABC       11-13-2012
    06            product3           002XYZ       11-14-2012
    07            product11          002XYZ       11-14-2012

Now what I need is if I supply a USERID like 001ABC
I need the output to be a 1 if the USERID matches the one I supply and(which it should automatically)it appears in the product table and I need it to show a 0 if it just appears in the products table

So two examples of the above two tables and these two USERIDs would look like this

USERID 001ABC supplied
yields

  OUTPUT
  1
  0
  0
  0
  1
  0
  1
  0
  0
  0
  0
  1

USERID 002XYZ supplied
yields

  OUTPUT
  1
  0
  1
  0
  0
  0
  0
  0
  0
  0
  1
  0

Using CASE statements has failed or I was not getting the syntax correct
I am using PHP and MYSQL

My current query worked good as long as I had a single USERID but failed when I tried filtering by the userID as well

PHP/MYSQL query:

    SELECT (PURCHASES.PRODUCT_NAME IS NOT NULL) AS purchased 
    FROM PRODUCTS 
      LEFT JOIN PURCHASES 
      ON PRODUCT_NAME = PRODUCT_NAME ORDER BY 1

I am not sure what I am doing wrong.

When I added another user with two purchases the results seemed to simply add two more rows to the output so the output would have had 14 rows instead of the original 12 as in the examples I show.

How can I can get a single column output with a total amount of records that equals the total amount of products each row set to zero except when a match is found in the purchases table identified by the product name then instead of zero a 1 is in the output.

Answer 1

Here’s the query you want. You need to order the results by the product ID; you’re ordering them by the 0/1 value in the output column, which of course destroys the usefulness of that column.

You also need to do a summary on the filtered purchases table to figure out whether there have been any purchases of the specific product. That’s the subquery “b”.

Finally, you left join from products to purchases, because you want exactly one row in your output resultset for each product.

     select ifnull(b.number>0,0) output
       from products a
  left join (
              select count(*) number,
                     product_name
                from purchases
               where userid = '001ABC'
            group by product_name
           ) b on a.product_name = b.product_name
  order by a.product_id

See this SQL Fiddle for example. http://sqlfiddle.com/#!2/6e985/12/0