On Tue, Jan 2, 2018 at 4:15 PM, petern <peter.nichvolo...@gmail.com> wrote:
> Hi Tony. Good. Yes, simpler test case is always better when posting
> possible bugs.
>
> Unfortunately, as Cezary points out, this error is by design (from
> select.c):
>
> if( pFunc->iDistinct>=0 ){
> Expr *pE = pFunc->pExpr;
> assert( !ExprHasProperty(pE, EP_xIsSelect) );
> if( pE->x.pList==0 || pE->x.pList->nExpr!=1 ){
> sqlite3ErrorMsg(pParse, "DISTINCT aggregates must have exactly one "
> "argument");
> pFunc->iDistinct = -1;
> }else{
>
> It would be interesting to understand the harm avoided by disallowing
> DISTINCT scope of all the aggregate parameters. Probably slower, but what
> else? Usually, there is a comment in the source but not for this one.
I'm not the guy who wrote it or decided how it should work, but it
seems to me that "group_concat(distinct x,y)" would not work
intuitively if y is a variable, though (somewhat surprisingly to me)
it works:
sqlite> create table t(x,y);
sqlite> insert into t values (1,','),(1,'+'),(2,'.'),(2,'-');
sqlite> select group_concat(x,y) from t;
1+1.2-2
sqlite> select group_concat(distinct x,y) from t;
Error: DISTINCT aggregates must have exactly one argument
sqlite> select group_concat(x,y) from (select distinct x, y from t);
1+1.2-2
Are there other aggregate functions that take multiple arguments? I
can't find any examples online of aggregates that take more than one,
which seems like the normal way something like this would be done.
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