What does TOP mean ?

[Dave Morris]

On 2015-04-27 16:03, Markus Demleitner wrote:
> 
> And regarding Walter's interjection:
> 
>> I thought that the difference between MAXREC and TOP is that MAXREC
>> requires an overflow indicator, while TOP would prohibit it.
> 
> Interesting thought -- is it intended to work this way? [it doesn't
> in DaCHS, and a quick search in the 1.1 specs didn't give me anything
> pointing in that direction]
> 

For a TAP service.

I don't know what the specifications say, but as an end user, I would 
expect that the server returns the lesser of the two, TOP or MAXREC.

However, if MAXREC caused the truncation, then that would be an 
overflow, if TOP cause the truncation, then it would not.

If TOP > MAXREC, then return MAXREC rows and flag an overflow. Which 
means this probably would hit MAXREC and return an overflow :

     SELECT TOP 1000000000000000000 * FROM table

If TOP < MAXREC, then return TOP rows and no overflow. So I would not 
expect to get an overflow for this :

     SELECT TOP 1 * FROM table

I would probably expect the other services to behave in a similar 
manner.

Hope this helps,
Dave

--------
Dave Morris
Software Developer
Wide Field Astronomy Unit
Institute for Astronomy
University of Edinburgh
--------