Question

I have two tables. One table looks like

ORDER_ID | SHOPPER_NAME | DATE
-------------------------------
001A     | Marianna     | 08/09/2012
002A     | Jason        | 80/08/2012

and another table that has information on the order

ORDER_ID | DATA_CODE   | DATA_VALUE
----------------------------------
001A     | MILK_MONEY  | 1.20
001A     | NUM_EGGS    | 22
002A     | TOTAL_SPENT | 32.43
001A     | TOTAL_SPENT | 42.13

I need to get several of the data codes for a specific order. How can I select SHOPPER_NAME, MILK_MONEY (DATA_VALUE where DATA_CODE = ‘MILK_MONEY’), TOTAL_SPENT and NUM_EGGS in one row? I have it working where I am doing 3 joins like

SELECT SHOPPER_NAME,
       MILK.DATA_VALUE,
       EGGS.DATA_VALUE,
       TOTAL.DATA_VALUE
FROM GROCERIES G
JOIN ORDER_INFO MILK ON MILK.ORDER_ID=G.ORDER_ID
JOIN ORDER_INFO EGGS ON EGGS.ORDER_ID=G.ORDER_ID
JOIN ORDER_INFO TOTAL ON TOTAL.ORDER_ID=G.ORDER_ID

However this is starting to look ugly and it does not feel right to be doing multiple joins on the same table. Is there a more efficient way of doing this?

Thank you!

Answer 1

You could use a pivot on your 2nd table to denormalize it somewhat or you could change your db architecture by denormalizing it a bit. Look up MySQL PIVOT on stack overflow for more examples, but something like this:

SELECT * FROM 
(SELECT ORDER_ID, DATA_CODE, DATA_VALUE FROM tablename
PIVOT (sum(DATA_VALUE) FOR DATA_CODE IN ([MILK_MONEY], [NUM_EGGS], [TOTAL_SPENT])) pvt