GROUP BY only rows with a certain condition and date

问题

I have a basic table in my database that has a simple transactions history such as depositing money to an account, withdrawing money, and having money refunded. Each entry has a date associated with it.

I have a php page that displays this transactional information row by row and it looks great. However, is there a way within the mySQL query that I can "collapse" all "refunded" money transactions into groupings by day? It's quite easy to do a GROUP_BY on the transaction type but I only want to group by on if the transaction_type is of type "refund" and those refunds happened on the same day. Thanks!

My Current Example Table:
Jan 3, Deposit, $100
Jan 3, Deposit, $200
Jan 2, Withdraw, $50
Jan 2, Refund, $100
Jan 2, Refund, $100
Jan 2, Deposit, $200
Jan 2, Refund, $100
Jan 1, Deposit, $100

How I would like the data to display
Jan 3, Deposit, $100
Jan 3, Deposit, $200
Jan 2, Withdraw, $50
Jan 2, Refund, $300 < this row has collapsed all Refunds for Jan 2nd into 1 row
Jan 2, Deposit, $200
Jan 1, Deposit, $100

The current SQL is something like:

SELECT transaction_date, transaction_type, transaction_amount
FROM transaction_history
WHERE customer_id = $customer_id
ORDER BY transaction_date DESC

回答1:

give this a try,

SELECT  transaction_date, transaction_type, SUM(transaction_amount)
FROM    TableName
-- WHERE customer_id = $customer_id
GROUP   BY transaction_date, 
           CASE WHEN transaction_type = 'refund' THEN 1 ELSE RAND() END
ORDER   BY transaction_date DESC

• SQLFiddle Demo

来源：https://stackoverflow.com/questions/18883366/group-by-only-rows-with-a-certain-condition-and-date