Re: Problems with query not using expeced indexes

[Rick James]

1. Don't quote values that correspond to INT columns; do quote columns that correspond to VARCHAR fields:
AND date_month = '200910'
AND customerid =1
(Or change the datatypes)

2. Use
dateDay >= '2009-10=01' AND dateDay < DATE_ADD(dateDay, INTERVAL 1 MONTH)

3.
INDEX(customerid, processed, dateDay)

4. Why are your grouping by customer id but not displaying it?

All together:

# do once:
ALTER TABLE daily
   ADD INDEX (customerid, processed, dateDay);
# then...
SELECT  SUM( price ) AS total_price,
        DATE_FORMAT(dateDay, '%Y%m') AS date_month
    FROM  daily
    WHERE  processed = 0
      AND  dateDay >= '2009-10=01'
      AND  dateDay < DATE_ADD(dateDay, INTERVAL 1 MONTH)
      AND  customerid = '1'
    GROUP BY  2;