[gdal-dev] OGR SQL, COUNT([DISTINCT] xx) and NULL values

[Even Rouault]

Le vendredi 25 novembre 2011 23:14:31, Even Rouault a écrit :
> Hi,
> 
> http://trac.osgeo.org/gdal/ticket/4354 :
> 
> """Currently, OGR SQL considers COUNT(a_column) as a synonym of COUNT(*).
> However the standard mandates that COUNT(a_column) only count non-NULL
> values, whereas COUNT(*) count all rows (after the effect of WHERE clause
> of course). So COUNT(a_column) should not be considered as equivalent to
> COUNT(*) The same applies for COUNT(DISTINCT a_column): it should only
> count unique non-NULL values.
> What is a bit annoying here is that ogr_sql.html says that : "As a special
> case, the COUNT() operator can be given a "*" argument instead of a field
> name which is a short form for count all the records though it would get
> the same result as giving it any of the column names [...]"
> If we fix the current behaviour to be conformant with the standard, it can
> break assumptions made by users. But currently, there's an inconsistency if
> you look at the result of -sql "select sum(foo), count(foo), avg(foo) from
> bar" when there are null values.
> """
> Perhaps only fix that in trunk (the current behaviour existed in 1.7 and
> likely previous versions, not only in 1.8) ? and in the doc, add a note
> about the difference between new and old behaviour ?

Commited in trunk only

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