Hi,
While thinking about this in the morning yesterday, I came up with a solution. First let me explain a bit more about the challenge.
I was implementing percentile_cont for a contract project. I added the syntax to the parser. On the backend I was using dense_rank as my initial template. Because dense_rank takes ANY_1, it would receive either a flt or int BAT. I thought i had everything working great until i worked with a decimal column. Because the decimal type is just an int type scaled, and the BAT doesn't record this, I was stuck. The window function generates a result based on the values (vs dense_rank just needing to know ordinality)
My solution was to modify the AST after the parse to inject a CAST to a dbl on the OVER portion. It was not my ideal solution, since it will force an intermediate to be created for any type that isn't a double. None the less, the MAL optimizers work correctly and the function handles all types.
Best,
Dru
On Sat, Nov 9, 2013 at 8:22 AM, Lefteris lsidir@gmail.com wrote:
I second that! Are you sure that you cannot come up with an alternative algorithm for your aggregation that does not need this information (and possibly be faster) ?
On Sat, Nov 9, 2013 at 11:26 AM, Stefan Manegold Stefan.Manegold@cwi.nl wrote:
Hi Dru,
the decimal scale information is only maintained in the SQL catalog and given that decimals are stored as integers in MonetDB, neither the
MonetDB
kernel, nor MAL usually need to know about decimals or their scale.
Hence, the question is, whether/why your aggregate functions would need
to
know about decimals or their scale?
Best, Stefan
Dru Nelson drudru@gmail.com wrote:
HI,
I"m working on writing an aggregate in in C that is a MAL function. I've run into a problem with decimal types.
I've noticed that when I inspect the BAT inputs for various types, they are coerced to simpler types. (flt,dbl -> dbl). (int, decimal -> int). There is also no other information in the BAT structure to see the type.
I notice that a SQL select gets the type info passed in as parameters
for
the 'exportValue' output.
For example:
sql.exportValue(1,".","second_single_value","decimal",9,3,8,_4,"");
How can I get this type information ('decimal', etc.) passed into my function?
Dru
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