Question

I have a transaction table, and a tag table. I want to get a sum of all transactions in the transaction table grouped by tag. There are two different types of transaction: “budget” and “actual”

This query will return me what I want for “budget” transactions:

  SELECT tg.name as tag, SUM(amount) as budgetTotal 
    FROM transaction tx
    JOIN transaction_tag tt ON tt.transaction_id = tx.id
    JOIN tag tg ON tg.id = tt.tag_id
   WHERE tx.type = "budget"
     AND tx.date >= '2011-07-15' 
     AND tx.date < '2011-08-15'
GROUP BY tg.name

And of course pretty much the same query for “actual” transactions:

  SELECT tg.name as tag, SUM(amount) as actualTotal 
    FROM transaction tx
    JOIN transaction_tag tt ON tt.transaction_id = tx.id
    JOIN tag tg ON tg.id = tt.tag_id
   WHERE tx.type = "actual"
     AND tx.date >= '2011-07-15' 
     AND tx.date < '2011-08-15'
GROUP BY tg.name

My question: how do I group the results of these two queries, into one, so I get one results table with three columns: tag, budgetTotal and actualTotal?

Answer 1

Try this:

  SELECT tg.name, 
         CASE WHEN tx.type = "actual" THEN SUM(amount) END AS actualTotal,
         CASE WHEN tx.type = "budget" THEN SUM(amount) END AS budgetTotal
  FROM....
  WHERE  tx.type IN ("actual", "budget")
  AND   ....
  GROUP BY tg.name