I wanted to know if it's possible to attempt to deallocate a PostgreSQL prepared statement before trying to open it
at the moment I am using the following code to deallocate all prepared statements
cur_deallocate = gv_pgsql.cursor()
cur_deallocate.execute("deallocate all")
cur_users = gv_pgsql.cursor()
cur_users.execute("prepare cur_users as " +
"select * from users")
this works however if there is another prepared statement that I still need in a separate function then it will be closed as well. However if I use deallocate cur_users then the program will crash with the error that it can't deallocate a prepared statement that doesn't exist.
Is there a way around this? to attempt to deallocate and if it fails then prepare the statement
Catch the error in an except block, or see if it exists first using pg_prepared_statements view: enter link description here
In our installation statement names are stored in lower case
def safe_deallocate(self, statement_name):
curs.execute(
"select true from pg_prepared_statements where name = lower(%s)", (statement_name,))
if curs.rowcount:
curs.execute("deallocate {}".format(statement_name))
Related
Setup:
Oracle DB running on a windows machine
Mac connected with the database, both in the same network
Problem:
When I created a sequence in SQL Developer, I can see and use the sequence in this session. If I logoff and login again the sequence is still there. But if I try to use the sequence via Python and cx_Oracle, it doesn't work. It also doesn't work the other way around.
[In SQL Developer: user: uc]
create SEQUENCE seq1;
select seq1.nextval from dual; ---> 1
commit; --> although the create statement is a DDL method, just in case
[login via Python, user: uc]
select seq1.currval from dual;--> ORA-08002 Sequence seq1.currval isn't defined in this session
The python code:
import cx_Oracle
cx_Oracle.init_oracle_client(lib_dir="/Users/benreisinger/Documents/testclients/instantclient_19_8", config_dir=None, error_url=None, driver_name=None)
# Connect as user "hr" with password "hr" to the "orclpdb" service running on a remote computer.
connection = cx_Oracle.connect("uc", "uc", "10.0.0.22/orcl")
cursor = connection.cursor()
cursor.execute("""
select seq1.currval from dual
""")
print(cursor)
for seq1 in cursor:
print(seq1)
The error says, that [seq1] wasn't defined in this session, but why does the following work:
select seq1.nextval from dual
--> returns 2
Even after issuing this, I can't use seq1.currval
Btw., select sequence_name from user_sequences returns seq1in Python
[as SYS user]
select * from v$session
where username = 'uc';
--> returns zero rows
Why is seq1 not in reach for the python program ?
Note: With tables, everything just works fine
EDIT:
also with 'UC' being upper case, no rows returned
first issuing
still doesn't work
Not sure how to explain this. The previous 2 answers are correct, but somehow you seem to miss the point.
First, take everything that is irrelevant out of the equation. Mac client on Windows db: doesn't matter. SQLDeveloper vs python: doesn't matter. The only thing that matters is that you connect twice to the database as the same schema. You connect twice, that means that you have 2 separate sessions and those sessions don't know about each other. Both sessions have access to the same database objects, so you if you execute ddl (eg create sequence), that object will be visible in the other session.
Now to the core of your question. The oracle documentation states
"To use or refer to the current sequence value of your session, reference seq_name.CURRVAL. CURRVAL can only be used if seq_name.NEXTVAL has been referenced in the current user session (in the current or a previous transaction)."
You have 2 different sessions, so according to the documentation, you should not be able to call seq_name.CURRVAL in the other session. That is exactly the behaviour you are seeing.
You ask "Why is seq1 not in reach for the python program ?". The answer is: you're not correct, it is in reach for the python program. You can call seq1.NEXTVAL from any session. But you cannot invoke seq1.NEXTVAL from one session (SQLDeveloper) and then invoke seq1.CURRVAL from another session (python) because that is just how sequences works as stated in documentation.
Just to confirm you're not in the same session, execute the following statement for both clients (SQLDeveloper and python):
select sys_context('USERENV','SID') from dual;
You'll notice that the session id is different.
CURRVAL returns the last allocated sequence number in the current session. So it only works when we have previously executed a NEXTVAL. So these two statements will return the same value when run in the same session:
select seq1.nextval from dual
/
select seq1.currval from dual
/
It's not entirely clear what you're trying to achieve, but it looks like your python code is executing a single statement for the connection, so it's not tapping into an existing session.
This statement returns zero rows ...
select * from v$session
where username = 'uc';
... because database objects in Oracle are stored in UPPER case (at least by default, but it's wise to stick with that default. So use where username = 'UC' instead.
Python established a new session. In it, sequence hasn't been invoked yet, so its currval doesn't exist. First you have to select nextval (which, as you said, returned 2) - only then currval will make sense.
Saying that
Even after issuing this, I can't use seq1.currval
is hard to believe.
This: select * From v$session where username = 'uc' returned nothing because - by default - all objects are stored in uppercase, so you should have ran
.... where username = 'UC'
Finally:
commit; --> although the create statement is a DDL method, just in case
Which case? There's no case. DDL commits. Moreover, commits twice (before and after the actual DDL statement). And there's nothing to commit either. Therefore, what you did is unnecessary and pretty much useless.
Using Python and SQlite3 where c is a cursor this code...
print("vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv")
print("SQL and parameters:",sql,parm)
c.execute(sql,parm)
# Get the row
print("Executed OK")
response = c.fetchone()
# If not successful return null
if not response:
return None
#
print("and produced ", response)
print("^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^")
give this output:
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
SQL and parameters: select * from Links where LinkNum = ? (301,)
Executed OK
and produced (301, 'Index', 'The Independent', 'https://www.independent.co.uk/', 6, 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
SQL and parameters: select * from Links where LinkNum = ? (301,)
Encountered exception of type ProgrammingError with arguments ('Incorrect number of bindings supplied. The current statement uses 1, and there are 6 supplied.',)
The application will close
Two identical statements. 1 works and the next throws the exception. As can be seen the row I'm trying to retrieve has 6 columns but that's the only hint/clue I can see. Can anyone help with tracking down the problem? Thanks.
Whatever was causing SQLite to have a fit I remedied the problem by retrieving the second row/object out side the Links object and passing it as an argument to the method I was calling, rather than have that method attempt to retrieve the object.
The problem would still be there but must be deep within the internals of Python instantiation and/or SQLite. Whatever, this problem is solved with some less fancy code.
So I have an issue very similar to this question, but a bit different.
I am calling cursor.execute(sqlString) on a piece of sql that works fine when I run it directly on the mysql workbench. When I run the code however I get no result set.
I have exactly the same issue symptons as stated in the link and I have tried the linked solutions but it turns out that I do not have the same issue.
my _stored_results[] is empty when returning.
I am using the code in a try/except block, I have another python program that uses the same code to load a csv into a my mySQL db and it works dandy.
The code where I am having the issue is within an #app.route if that makes any differnce.
My code looks like this:
def functionName() :
try:
import mysql.connector
from mysql.connector import errorcode
cnx = mysql.connector.connect(user=init["dbDetails"][0], password=init["dbDetails"][1], host=init["dbDetails"][2], database=init["dbDetails"][3])
cur = cnx.cursor()
cur.close() #I deffo don't need the two lines below but they were added for a sanity check, just to make sure the cur was not being read from any other code.
cur = cnx.cursor() # and this one obviously
sqlString = 'CALL `schemaName`.`getProcedureName_sp`(1, 1, 0)'
cur.execute(sqlString, multi=True) # tried it here without the multi=True and got the msg telling me to use it.
getSomeDetails = cur.fetchall()
cnx.commit() # probably don't need to commit here I am just reading from the dB but I am trying anything as I have no idea what my issue might be.
return render_template('success.html')
except Exception as e:
return render_template('error.html', error = str(e))
finally:
cur.close()
cnx.close()
I am so baffled as I have this same code working in several places.
So I was beating my head against the wall with this, and when I couldn't get anywhere, I just decided to leave it and move on, then come back with a fresh mind. Well... It worked, kinda.
So I haven't found the solution but I have found a work around that does the job and might even shed some light as to what is actually happening in my code.
I decided that as the fetchall() method was what was causing me the trouble I should try to circumvent it.
I probed the cursor(cur) just before the fetchall() method was called and saw that cur._rows contains the results from the SQL call.
So I changed the line
getSomeDetails = cur.fetchall()
to
if len(cur._rows) > 0 :
getSomeDetails = list(cur._rows[0]) #I only ever expect one result in this query
#getSomeDetails should now have the row I am looking for
getSomeDetails[0] #gets me the field I am looking for
and now my variable getSomeDetails has the return values from the procedure call
They are however not in the nice format that I should have gotten them from the fetchall() function, so I had to do some processing, I had to ensure that I was getting some values back and I noted that these values were returned in a tuple
I have come across this issue on two different machines running two different OS's and two different versions of python (Windows 7 with Python 2.7 and Windows 10 with Python 3) both pieces of code were different so obviously infact I was using two different MySQL libraries so the actual code for the fix was slightly different in both cases but I am now in both cases getting data from my DB into variables in Python, so that's cool.
However, this is a hack and I am aware of that, I would rather be using the proper function cur.fetchall() so I am still open to suggestions of what could be going wrong here.
I have a python program which uses pypyodbc to interact with MSSQL database. A stored procedure is created in MSSQL and is run via python. If I execute the stored procedure only once (via python), there are no problems. However, when it is executed multiple times within a for loop, I get the following error:
pypyodbc.ProgrammingError: ('24000', '[24000] [Microsoft][SQL Server Native Client 11.0]Invalid cursor state')
My python code details are below:
connection_string_prod = 'Driver={SQL Server Native Client 11.0};Server=PSCSQCD1234.TEST.AD.TEST.NET\SQLINS99,2222;Database=Test;Uid=python;Pwd=python;'
connection_prod = pypyodbc.connect(connection_string_prod)
cursor_prod = connection_prod.cursor()
get_files_to_load_query = "Get_Files_To_Load"
files_to_load = cursor_prod.execute(get_files_to_load_query)
for file_name in files_to_load:
load_query = "Load_Query_Stored_Proc #File_Name = '" + file_name + "'"
cursor_prod.execute(load_query)
cursor_prod.commit()
cursor_prod.close()
connection_prod.close()
In some posts it was suggested to use "SET NOCOUNT ON" at the top of the SQL stored procedure. I've done that already and it did not help with this issue.
Below is a code of a simple stored procedure that is causing the issue:
CREATE PROCEDURE [dbo].[Test]
AS
SET NOCOUNT ON
INSERT INTO Test(a)
SELECT 1
Why executing the stored procedure within a for loop only causes an issue?
Please advise.
Thank you!
You are using cursor_prod values to control the for loop and then using that same cursor object inside the loop to run the stored procedure, thus invalidating the previous state of the cursor for controlling the loop. The first iteration of the loop is where the cursor gets overwritten, which is why you don't encounter the error until you try to go through the loop a second time.
You don't need to create a second connection, but you do need to use a second cursor to execute the stored procedure. Or, you could use .fetchall to stuff all of the file names into a files_to_load list and then iterate over that list, freeing up the cursor to run the stored procedure.
I am trying to call dbms_random.seed(42) on my DB, see ref. I need to use python and the JayDeBeApi connector. So far I've only been able to execute select statement without issue. I fail to understand what I am doing wrong.
It seems that JayDeBeApi does not provide the callproc method, so I cannot use it:
AttributeError: 'Cursor' object has no attribute 'callproc'
I've naively tried:
conn = jaydebeapi.connect('oracle.jdbc.driver.OracleDriver',
['jdbc:oracle:thin:#server:1521/dbname', 'user', 'password'])
curs = conn.cursor()
sql="exec dbms_random.seed(42)"
curs.execute(sql)
but this leads to: Error: ORA-00900: invalid SQL statement
I've tried two solutions which seems to have correct syntax, but since the generator is not deterministic, I believe they actually failed:
Using begin/end:
sql="begin dbms_random.seed(42); end;"
curs.execute(sql)
Using call:
sql="{ call dbms_random.seed(42) }"
curs.execute(sql)
So my question is: how do I call dbms_random.seed(42) on Oracle using JayDeBeApi ? As a side question how do I check that a statement has actually failed to execute (no exception was thrown and return value for execute is undefined.)
Update:
In fact the seed initialization is working as expected, since the results are what I expect for:
sql="SELECT DBMS_RANDOM.value FROM dual"
curs.execute(sql)
data = curs.fetchall()
print(data)
However I still see some odd behavior for my random query selection:
SELECT *
FROM (
SELECT *
FROM table
ORDER BY DBMS_RANDOM.RANDOM)
WHERE rownum < 21;
For some reason in the latter case, the DBMS_RANDOM.RANDOM is actually random...
After multiple trial and error, I believe this is just a side effect. Since I was not doing the cleanup pass:
curs.close()
conn.close()
jpype.shutdownJVM()
The query would lead to somewhat undefined behavior. Now that I have a proper cleanup code, I am getting deterministic results when calling multiples times my python script.