I work with Oracle database and cx_oracle. The problem I have is that when I have a query, it returns the wrong answer in cx_oracle. But this query is the correct answer in SQL developer. What is my problem?
This is my query:
select id from my_table
in sql developer we have the right result, but
Returns deleted records in cx_oracle.It looks like the records is cached and returned.
You might not COMMITED the delete on SqlDeveloper.
Related
I want to list and describe the tables present in an Oracle database.
To do this by connecting to the database with a client such as SQL Plus, a working approach is:
List the tables:
select tablespace_name, table_name from all_tables;
Get columns and data types for each table:
describe [table_name];
However when using cx_Oracle through python, cur.execute('describe [table_name]') results in an 'invalid sql' error.
How can we use describe with cx_Oracle in python?
It seems you can't.
From cx_Oracle instead of describe use:
cur.execute('select column_name, data_type from all_tab_columns where table_name = [table_name]')
(From Richard Moore here http://cx-oracle-users.narkive.com/suaWH9nn/cx-oracle4-3-1-describe-table-query-is-not-working)
As noted by others there is no ability to describe directly. I created a set of libraries and tools that let you do this, however. You can see them here: https://github.com/anthony-tuininga/cx_OracleTools.
I'm new to sqlalchemy and have been trying to figure this out for days!
I have some python code which is executing the following line:
mdb_session.query(PendingConfig).filter(PendingConfig.id == config.id).delete()
It's deleting all rows in a table called PendingConfig which have an id equals to a given config.id.
I want to log the underlying SQL query sqlalchemy that generates, but don't know how to do that since delete() returns an integer equal to the number of rows deleted.
I tried setting up a logger but that had it's own issues, as I explained in this post.
Need help on this!
If you really want to get the SQL that was actually run by the MySQL server, then you can enable the MySQL query log or slow query log, and read it from the database server.
See https://dev.mysql.com/doc/refman/5.7/en/slow-query-log.html
The MySQL Server doesn't know anything about Python, it just knows that a client sent it a query to execute.
If it's a parameterized query, it will contain ? placeholders in the SQL text, but SQLAlchemy doesn't do placeholders as far as I know. It always interpolates parameter values into the SQL query before sending it to MySQL.
I want to come up minimal set of queries/loc that extracts the table metadata within a database, on as many versions of database as possible. I'm using PostgreSQl. I'm trying to get this using python. But I've no clue on how to do this, as I'm a python newbie.
I appreciate your ideas/suggestions on this issue.
You can ask your database driver, in this case psycopg2, to return some metadata about a database connection you've established. You can also ask the database directly about some of it's capabilities, or schemas, but this is highly dependent on the version of the database you're connecting to, as well as the type of database.
Here's an example taken from http://bytes.com/topic/python/answers/438133-find-out-schema-psycopg for PostgreSQL:
>>> import psycopg2 as db
>>> conn = db.connect('dbname=billings user=steve password=xxxxx port=5432')
>>> curs = conn.cursor()
>>> curs.execute("""select table_name from information_schema.tables WHERE table_schema='public' AND table_type='BASETABLE'""")
>>> curs.fetchall()
[('contacts',), ('invoicing',), ('lines',), ('task',), ('products',),('project',)]
However, you probably would be better served using an ORM like SQLAlchemy. This will create an engine which you can query about the database you're connected to, as well as normalize how you connect to varying database types.
If you need help with SQLAlchemy, post another question here! There's TONS of information already available by searching the site.
I have a python script that connects to a local MySQL db. I know it is connecting correctly because I can do this and get the proper results:
cursor.execute("SELECT * FROM reel")
But when I try to do any insert statements it just does nothing. No error messages, no exceptions. Nothing shows up in the database when I check it from sqlyog. This is what my code looks like:
self.cursor.executemany("INSERT INTO reel (etime,etext) VALUES (%s,%s)", tups)
where tups is a list of tuples looking like this ('0000-00-00 00:00:00','text'). No errors show up and if I copy paste the generated SQL query into sqlyog it works. I've tried generating the query and doing cursor.execute() on it and no errors and no result either. Anyone know what I'm doing wrong?
You need to do a self.cursor.commit() after self.cursor.executemany("INSERT INTO reel (etime,etext) VALUES (%s,%s)", tups)
Starting with 1.2.0, MySQLdb disables autocommit by default, as required by the DB-API standard (PEP-249). If you are using InnoDB tables or some other type of transactional table type, you'll need to do connection.commit() before closing the connection, or else none of your changes will be written to the database.
Conversely, you can also use connection.rollback() to throw away any changes you've made since the last commit.
Important note: Some SQL statements -- specifically DDL statements like CREATE TABLE -- are non-transactional, so they can't be rolled back, and they cause pending transactions to commit.
Is a FAQ
I'm new to Python and Python's MySQL adapter. I'm not sure if I'm missing something obvious here:
db = MySQLdb.connect(# db details omitted)
cursor = self.db.cursor()
# WORKS
cursor.execute("SELECT site_id FROM users WHERE username=%s", (username))
record = cursor.fetchone()
# DOES NOT SEEM TO WORK
cursor.execute("DELETE FROM users WHERE username=%s", (username))
Any ideas?
I'd guess that you are using a storage engine that supports transactions (e.g. InnoDB) but you don't call db.commit() after the DELETE. The effect of the DELETE is discarded if you don't commit.
See http://mysql-python.sourceforge.net/FAQ.html#my-data-disappeared-or-won-t-go-away:
Starting with 1.2.0, MySQLdb disables
autocommit by default, as required by
the DB-API standard (PEP-249). If you
are using InnoDB tables or some other
type of transactional table type,
you'll need to do connection.commit()
before closing the connection, or else
none of your changes will be written
to the database.
See also this similar SO question: Python MySQLdb update query fails
Perhaps you are violating a foreign key constraint.
To your code above,
just add a call to self.db.commit().
The feature is far from an annoyance:
It saves you from data corruption issues
when there are errors in your queries.
The problem might be that you are not committing the changes. it can be done by
conn.commit()
read more on this here