从 Python 的 Redshift 过程调用返回数据

Question

redshift_connector is defined to be aligned with https://peps.python.org/pep-0249/#id24 but I can't, after calling procedure, retrieve data into a dataframe.

Instead I'm getting 'mycursor' value. How to overcome this?

fetch*() methods don't allow passing argument that will allow getting into data in mycursor .

I also tried RECORDS type but no luck.

Procedure's body :

--CREATE TABLE reporting.tbl(a int, b int);
--INSERT INTO reporting.tblVALUES(1, 4);

CREATE OR REPLACE PROCEDURE reporting.procedure(param IN integer, rs_out INOUT refcursor)
LANGUAGE plpgsql
AS $$

BEGIN
  OPEN rs_out FOR SELECT a FROM reporting.tbl;
END;
$$;

Python code :

import redshift_connector

conn = redshift_connector.connect(
     host='xyz.xyz.region.redshift.amazonaws.com',
     database='db',
     port=5439,
     user="user",
     password='p@@s'
)
  

cursor = conn.cursor()

cursor.execute("BEGIN;") 
res = cursor.callproc("reporting.procedure", parameters=[1, 'mycursor'])
res = cursor.fetchall()
cursor.execute("COMMIT;")

#returns (['mycursor'],)
print(res)

Answer 1

I think you are trying to define 2 cursors and only one is allowed. "conn.cursor()" creates a cursor with name defined by redshift_connector. "OPEN rs_out FOR SELECT a FROM reporting.tbl;" in your procedure opens a second cursor with the name mycursor. The "cursor.fetchall()" is trying to fetch from the first cursor (and possibly erroring). No command is fetching from mycursor.

I don't believe there is a way to get "cursor.fetchall()" to point to a different cursor name so I think you need to run the SQL commands (CALL, FETCH, etc) directly.

Something like this:

import redshift_connector

conn = redshift_connector.connect(
     host='xyz.xyz.region.redshift.amazonaws.com',
     database='db',
     port=5439,
     user="user",
     password='p@@s'
)

conn.run("BEGIN;") 
res = conn.run("CALL reporting.procedure(1, 'mycursor')")
res = conn.run("FETCH ALL FROM mycursor;")
conn.run("COMMIT;")

print(res)

Be aware that if you are on a single node Redshift cluster FETCH ALL isn't allowed and you will need to use FETCH FORWARD instead.

Above untested and off the cuff.