Tom Lane wrote:
> Shilong Stanley Yao <yao(at)noao(dot)edu> writes:
>
>>I am trying to write a function in Postgresql, which takes 2 floats and
>>returns a box. But seems the nested single-quote in the AS clause
>>prevent $1 and $2 from being expanded. Besides writing a C function
>>instead of a SQL one, is there any way to solve this problem?
>
>
>>CREATE OR REPLACE FUNCTION func_radec_to_box(float, float) RETURNS box
>> AS 'SELECT box \'(($1, $2), (1.3, 1.4))\''
>> LANGUAGE 'sql'
>> WITH (ISCACHABLE);
>
>
> This is never going to work because you are trying to use the
> typed-literal syntax with something that you don't actually want to
> be a literal constant. You need to think in terms of a function, not
> a literal. In this case I think what you want is the box-from-two-points
> constructor function, together with the point-from-two-floats constructor:
>
> ... AS 'SELECT box(point($1, $2), point(1.3, 1.4))'
>
> If you had a mind to, you could write the constant point as a literal:
>
> ... AS 'SELECT box(point($1, $2), point \'1.3, 1.4\')'
>
> but you can't write the variable point as a literal.
>
> regards, tom lane
Thank you very much for this nice solution. It worked very well!
BTW, a spatial query involving RTREE indexes showes that SQL function is
much slower than C function, which is within the expectation.
Thanks everyone of the previous responses for your help too!
Stan