How to convert a PL/PgSQL procedure into a dynamic one? - postgresql

Question

I am trying to write a plpgsql procedure to perform spatial tiling of a postGIS table. I can perform the operation successfully using the following procedure in which the table names are hardcoded. The procedure loops through the tiles in tile_table and for each tile clips the area_table and inserts it into split_table.
CREATE OR REPLACE PROCEDURE splitbytile()
AS $$
DECLARE
tile RECORD;
BEGIN
FOR tile IN
SELECT tid, geom FROM test_tiles ORDER BY tid
LOOP
INSERT INTO split_table (id, areaname, ttid, geom)
SELECT id, areaname, tile.tid,
CASE WHEN st_within(base.geom, tile.geom) THEN st_multi(base.geom)
ELSE st_multi(st_intersection(base.geom, tile.geom)) END as geom
FROM area_table as base
WHERE st_intersects(base.geom, tile.geom);
COMMIT;
END LOOP;
END;
$$ LANGUAGE 'plpgsql';
Having tested this successfully, now I need to convert it to a dynamic procedure where I can provide the table names as parameters. I tried the following partial conversion, using format() for inside of loop:
CREATE OR REPLACE PROCEDURE splitbytile(in_table text, grid_table text, split_table text)
AS $$
DECLARE
tile RECORD;
BEGIN
FOR tile IN
EXECUTE format('SELECT tid, geom FROM %I ORDER BY tid', grid_table)
LOOP
EXECUTE
FORMAT(
'INSERT INTO %1$I (id, areaname, ttid, geom)
SELECT id, areaname, tile.tid,
CASE WHEN st_within(base.geom, tile.geom) THEN st_multi(base.geom)
ELSE st_multi(st_intersection(base.geom, tile.geom)) END as geom
FROM %2$I as base
WHERE st_intersects(base.geom, tile.geom)', split_table, in_table
);
COMMIT;
END LOOP;
END;
$$ LANGUAGE 'plpgsql';
But it throws an error
missing FROM-clause entry for table "tile"
So, how can I convert the procedure to a dynamic one? More specifically, how can I use the record data type (tile) returned by the for loop inside the loop? Note that it works when format is not used.

Answer 1

You can use EXECUTE ... USING to supply parameters to a dynamic query:
EXECUTE
format(
'SELECT r FROM %I WHERE c = $1.val',
table_name
)
INTO result_var
USING record_var;
The first argument to USING will be used for $1, the second for $2 and so on.
See the documentation for details.

Answer 2

Personally I use somehow different way to create dynamic functions. By concatination and execute function. You can also do like this.
CREATE OR REPLACE FUNCTION splitbytile()
RETURNS void AS $$
declare
result1 text;
table_name text := 'test_tiles';
msi text := '[phone]';
msi text := 'Hello world';
code text := 'code_name';
_operator_id integer := 2;
begin
query1 := 'SELECT msisdn from ' || table_name || ' where msisdn = ''' || msi::text ||''';';
query2 := 'INSERT INTO ' || table_name || '(msisdn,usage,body,pr_code,status,sent_date,code_type,operator_id)
VALUES( ''' || msi::text || ''',' || true || ',''' || _body::text || ''',''' || code::text || ''',' || false || ',''' || time_now || ''',' || kod_type || ',' || _operator_id ||');';
execute query1 into result1;
execute query2;
END;
$function$
You just make your query as text then anywhere you want you can execute it. Maybe by checking result1 value inside If statement or smth like that.