sql: DROP FUNCTION does not drop a function

[mgartner]

DROP FUNCTION does not fully drop a UDF:

defaultdb> CREATE FUNCTION fn(a INT) RETURNS INT LANGUAGE SQL AS 'SELECT a';
CREATE FUNCTION

defaultdb> SELECT fn(1);
  fn
------
   1
(1 row)

defaultdb> DROP FUNCTION fn;
DROP FUNCTION

defaultdb> SELECT fn(1);
  fn
------
   1
(1 row)

It seems like the function is partially dropped, because I can create a function with the same name and arguments after the DROP, but the behavior of the original version of the function remains:

defaultdb> CREATE FUNCTION fn(b INT) RETURNS INT LANGUAGE SQL AS 'SELECT 33';
CREATE FUNCTION

defaultdb> SELECT fn(1);
  fn
------
   1
(1 row)

Jira issue: CRDB-22148

[mgartner]

cc @chengxiong-ruan for triage

[chengxiong-ruan]

@mgartner Looks like it's because the query select fn(1) is cached somehow :(
if you do select fn(2) after the drop or new create, it works alright heh.