Noel Frankinet wrote:
I would like to create a user function to know if a record is
contained in a rectangle ?
If have looked to sqlite_create_function
I know that my record has for column (xmin,ymin,xmax,ymax)
I would like to use the new function to write something like
select * from table where ??? contains ???? (how I pass the selecting
rectangle)
Is it possible ?
How do I do that ?
Thank you
Noel,
You need to create a predicate function that returns a boolean or
integer (0 or 1) value based on 6 input values. Conceptually it would
look like this:
int point_in_rect(px, py, rxl, rxh, ryl, ryh)
Where px and py are the location of a point, rxl and rxh are the low and
high limits of the rectangle's x dimension, and ryl and ryh are the low
and high limits of the rectangle's y dimension.
You would use this function like this:
create table points(x int, y int, data text);
select * from points where point_in_rect(x, y, 10, 100, 25, 75);
This should give you an idea of how to implement it using the sqlite APIs.
/* implement point in rect predicate function */
void point_in_rect(sqlite3_context* ctx, int argc, sqlite3_value** argv)
{
int p, rl, rh, in = 0;
/* check x values first */
p = sqlite3_value_int(argv[0]);
rl = sqlite3_value_int(argv[2]);
rh = sqlite3_value_int(argv[3]);
if (p >= rl && p <=rh) {
/* now check y values */
p = sqlite3_value_int(argv[1]);
rl = sqlite3_value_int(argv[4]);
rh = sqlite3_value_int(argv[5]);
if (p >= rl && p <= rh)
in = 1;
}
sqlite3_result_int(ctx, in);
}
/* register point in rect predicate */
sqlite3* db;
rc = sqlite3_create_function(db, "point_in_rect", 6,
SQLITE_UTF8, NULL, point_in_rect, NULL, NULL);
HTH
Dennis Cote
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