[BUG][cnosdb fdw] Using opengauss to query cnosdb fails when the tag is empty

[Benxiaohai001]

Describe the bug

Using opengauss to query cnosdb fails when the tag is empty

To Reproduce

cnosdb-cli

public ❯ CREATE TABLE air (visibility DOUBLE,temperature DOUBLE,pressure DOUBLE,TAGS(station));
Query took 0.002 seconds.

gsql

openGauss=# create foreign table air (time timestamp, visibility FLOAT8,temperature FLOAT8,pressure FLOAT8) server cnosdb_server options (tenant 'cnosdb', database 'public');
CREATE FOREIGN TABLE
openGauss=# INSERT INTO air (TIME, visibility, temperature, pressure) VALUES (now(), 56, 69, 411);
INSERT 0 1
openGauss=# INSERT INTO air (TIME, pressure) VALUES (now(),  411);
INSERT 0 1
openGauss=# select * from air;
ERROR:  Fail to request remote server: sql: SELECT time, visibility, temperature, pressure FROM public.air, reason: parse value error: ParseFloat

Expected behavior

No response

Additional context

No response

[Benxiaohai001]

The same problem exists with the missing time column

openGauss=# select * from air;
ERROR:  Fail to request remote server: sql: SELECT station, visibility, temperature, pressure FROM public.air, reason: parse value error: ParseFloat

[Benxiaohai001]

Null value problem solved

openGauss=# create foreign table air (time timestamp, visibility FLOAT8,temperature FLOAT8,pressure FLOAT8) server cnosdb_server options (tenant 'cnosdb', database 'public');
CREATE FOREIGN TABLE
openGauss=# INSERT INTO air (TIME, visibility, temperature, pressure) VALUES (now(), 56, 69, 411);
INSERT 0 1
openGauss=# INSERT INTO air (TIME, pressure) VALUES (now(),  411);
INSERT 0 1
openGauss=# select * from air;
            time            | visibility | temperature | pressure
----------------------------+------------+-------------+----------
 1970-01-01 00:00:00        |            |             |      411
 2024-04-19 16:30:38.119865 |         56 |          69 |      411
 2024-04-19 16:31:20.45643  |            |             |      411
 2024-04-22 11:31:42.164608 |         56 |          69 |      411
 2024-04-22 11:32:14.243136 |            |             |      411
 2024-04-19 16:23:20.916574 |         56 |          69 |      411
(6 rows)

openGauss=# drop foreign table air;
DROP FOREIGN TABLE
openGauss=# create foreign table air ( visibility FLOAT8,temperature FLOAT8,pressure FLOAT8) server cnosdb_server options (tenant 'cnosdb', database 'public');
CREATE FOREIGN TABLE
openGauss=# select * from air;
 visibility | temperature | pressure
------------+-------------+----------
            |             |      411
         56 |          69 |      411
            |             |      411
         56 |          69 |      411
            |             |      411
         56 |          69 |      411
(6 rows)

openGauss=# drop foreign table air;
DROP FOREIGN TABLE
openGauss=# create foreign table air ( time timestamp) server cnosdb_server options (tenant 'cnosdb', database 'public');
CREATE FOREIGN TABLE
openGauss=# select * from air;
            time
----------------------------
 1970-01-01 00:00:00
 2024-04-19 16:30:38.119865
 2024-04-19 16:31:20.45643
 2024-04-22 11:31:42.164608
 2024-04-22 11:32:14.243136
 2024-04-19 16:23:20.916574
(6 rows)

openGauss=#