I think adding a policy in Calcite to derive SUM's return type makes sense, as SQL standard seems not specify exactly what the return type of SUM should be. As a result, each system could choose to use different policy in the implementation.
Oracle seems to use "the same data type as the numeric data type of the argument" [1], while DB2 uses the policy "The result is a large integer if the argument values are small integers" [2]. [1] http://docs.oracle.com/database/121/SQLRF/functions196.htm#i89126 [2] http://public.dhe.ibm.com/ps/products/db2/info/vr101/pdf/en_US/DB2SQLRefVol1-db2s1e1011.pdf On Mon, Aug 10, 2015 at 2:05 PM, Julian Hyde <[email protected]> wrote: > Postgres return type is "bigint for smallint or int arguments, numeric for > bigint arguments, otherwise the same as the argument data type”[1] > > SQL Server return type is int for tinyint, smallint or int; bigint for > bigint[2]. > > I can see your point that “User demands the correct sum result”. But I’d > also be pissed with Postgres if it returned a numeric (arbitrary precision) > result when I am summing a bigint value. So I don’t think we’re going to > please everyone. > > I think the solution is to add the policy to derive SUM’s return type to > as a new method to RelDataTypeSystem. Then Kylin can supply its own. > > Julian > > [1] http://www.postgresql.org/docs/9.1/static/functions-aggregate.html < > http://www.postgresql.org/docs/9.1/static/functions-aggregate.html> > > [2] https://msdn.microsoft.com/en-us/library/ms187810.aspx < > https://msdn.microsoft.com/en-us/library/ms187810.aspx> > > > On Aug 9, 2015, at 8:09 PM, Li Yang <[email protected]> wrote: > > > >> 1. If x is an integer, what is the type of sum(x)? > > > > This is the key question. If calcite believes sum(int) = int, then Kylin > > have to find solution else where. User demands the correct sum result > > anyway. It's very hard to explain and justify the behavior to user, > > because other SQL engines like Postgres seem simply works... > > > > One workaround maybe let all initial values be bigint. > > > > On Sat, Aug 8, 2015 at 9:02 AM, Julian Hyde <[email protected]> wrote: > > > >> I would approach it a different way. There are 2 separate questions: > >> > >> 1. If x is an integer, what is the type of sum(x)? > >> > >> This concerns SQL query validation. Calcite’s answer is that if x has > type > >> T, then sum(x) has type T. Not perfect, but simple. If x is an int and > you > >> want the result to be a bigint, just write sum(cast(x as bigint)). > >> > >> 2. Do we detect overflow while calculating sum, and if so, how? > >> > >> This is an implementation question, and needs to be solved in each > engine. > >> Drill is one such engine, and Enumerable is another. Enumerable does not > >> currently detect overflow. > >> > >> One strategy would be to use a higher precision data type internally > (but > >> this strategy works only if you have an upper bound on the number of > input > >> rows). Another is to use a method such as java.lang.Math.addExact(int, > int). > >> > >> Julian > >> > >> > >> > >>> On Aug 7, 2015, at 10:38 AM, Jinfeng Ni <[email protected]> wrote: > >>> > >>> I think it makes sense to use bigint as the result type for > sum(integer). > >>> > >>> Postgres seems to work in this way. > >>> > >>> mydb=# \d+ emp > >>> Table "public.emp" > >>> Column | Type | Modifiers | Storage | Stats target | > >>> Description > >>> > >> > ----------+-----------------------+-----------+----------+--------------+------------- > >>> empno | integer | | plain | > | > >>> ..... > >>> > >>> create table tmp as select sum(empno) sum_eno from emp; > >>> > >>> \d+ tmp; > >>> Table "public.tmp" > >>> Column | Type | Modifiers | Storage | Stats target | Description > >>> ---------+--------+-----------+---------+--------------+------------- > >>> sum_eno | bigint | | plain | | > >>> > >>> > >>> As we can see, the column sum_eno in 'tmp' table after the CTAS > statement > >>> has bigint type. > >>> > >>> In Drill, we also use bigint for sum(integer). Drill has to put > >> additional > >>> logic, since Calcite by default will use int as the result type for > >>> sum(int). > >>> > >>> > >>> > >>> > >>> On Fri, Aug 7, 2015 at 6:51 AM, hongbin ma <[email protected]> > wrote: > >>> > >>>> hi, > >>>> > >>>> Suppose I have a table column called "price", its data type is > integer. > >>>> it seems that the sum aggregator in "select sum(price) from table" > will > >>>> return integer type, too. > >>>> > >>>> When I have millions of rows in the table, > >>>> "select sum(price) from table" might overflow, is it a bug? > >>>> Or may I how do you look into this problem? > >>>> > >>>> -- > >>>> Regards, > >>>> > >>>> *Bin Mahone | 马洪宾* > >>>> Apache Kylin: http://kylin.io > >>>> Github: https://github.com/binmahone > >>>> > >> > >> > >
