On Nov 3, 2011, at 3:31 PM, werner wrote: > Mark, > > On 11/03/2011 07:18 PM, Mark Erbaugh wrote: >> Using the query object count() method generates a sub-query (as per the >> docs). The docs say to use func.count to avoid the subquery. func.count >> seems to require a field object. Is there a way to generate a query that >> essentially becomes 'select count(*) from table' using the ORM, not the SQL >> generator? > Just the other day I thought I needed the same, initially I just used the > "id" column which all my tables had, but as count(anything) is pretty > expensive (using Firebird SQL - so might be different for other dbs) I wanted > to find a way without using count(). In my case I needed at some point to > get all the "id" values of that table (to build a virtual listctrl in > wxPython), so instead of doing the count and starting feeling the list I got > the "id" and did a len(onresult) to get my count. > > Point I am trying to make with a lot of words, maybe there is a solution > which doesn't need count() at all:-) .
I never considered that a count(*) was that expensive especially if there is no where clause. I would think that it would be less expensive than actually retrieving all the rows and counting them. What if there are millions of rows? The result set could fill up memory. In my case, I just need to know how many rows. I don't care about any other details. In one case, I'm checking to see if there are zero rows, in which case, I populate the table with initial rows. In another case, I'm just unittesting some code and I want to make sure that there are the proper number of rows in the table as one of the test conditions. Mark -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
