Character escape in "CREATE FUNCTION ..."

On Monday 15 March 2004 18:38, Shilong Stanley Yao wrote:

Dear All,
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);

If the box constructor is supposed to take a string, try something like:

SELECT box \'((\' || $1 || \'...etc

That is to say - use string concatenation

--
Richard Huxton
Archonet Ltd

On Mon, Mar 15, 2004 at 11:38:05 -0700,
Shilong Stanley Yao <yao@noao.edu> wrote:

Dear All,
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?

I believe you want to concatenate $1 and $2 with the constants parts
of the string rather than to embed them in the string.

The cube type in contrib/cube already has functions for making a cube
from float8 numbers without converting to text inbetween. Depending
on what you want this might be another approach for you.

Shilong Stanley Yao <yao@noao.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

Tom Lane wrote:

Shilong Stanley Yao <yao@noao.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