Re: [HACKERS] I think we need an explicit parsetree node for CAST

I have applied a patch for this one.

> I noticed today that the system drops any "typmod" modifier associated
> with a type name being casted to.  For example,
> 
> regression=# select '1.23456'::numeric(7,2);
>  ?column?
> ----------
>   1.23456            --- should be 1.23
> (1 row)
> 
> regression=# select CAST ('1234567.89' AS numeric(4,1));
>   ?column?
> ------------
>  1234567.89            --- should raise a numeric-overflow error
> (1 row)
> 
> These particular cases can be fixed with a one-line patch, I think,
> because there is storage in an A_Const node to hold a reference to
> a Typename, which includes typmod.  parse_expr.c is just forgetting
> to pass the typmod to parser_typecast().
> 
> BUT: there isn't any equally simple patch when the value being casted
> is not a constant.  For instance
> 
>     select field1 :: numeric(7,2) from table1;
> 
> cannot work properly now, because gram.y transforms it into
> 
>     select numeric(field1) from table;
> 
> which (a) drops the typmod and (b) bypasses all of the intelligence
> that should be used to determine how to coerce the type.
> 
> What I think we need is to add a new parsetree node type that explicitly
> represents a CAST operator, and then modify parse_expr.c to transform
> that node type into an appropriate function call (or, perhaps, nothing
> at all if the source value is already the right type).
> 
> Comments?
> 
>             regards, tom lane
> 
> ************
> 


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