For the record, I have looked into this, but cannot seem to figure out what is wrong.
So I'm doing the tutorial on web.py, and I get to the database part (can do everything above it). I wanted to use sqlite3 for various reasons. Since I couldn't figure out where to type the
sqlite3 test.db
line, I look into the sqlite3 module, and create a database with that. The code for that is:
import sqlite3
conn = sqlite3.connect("test.db")
print("Opened database successfully");
conn.execute('''CREATE TABLE todo
(id serial primary key,
title text,
created timestamp default now(),
done boolean default 'f');''')
conn.execute("INSERT INTO todo (title) VALUES ('Learn web.py')");
but I get the error
done boolean default 'f');''')
sqlite3.OperationalError: near "(": syntax error
I've tried looking into this, but cannot figure out for the life of me what the issue is.
I haven't had luck with other databases (new to this, so not sure on the subtleties), I wasn't able to just make the sqlite database directly so it might be a python thing, but it matches the tester.py I made with the sqlite with python tutorial...
Thanks if anyone can help me!
The problem causing the error is that you can't use the MySQL now() function here. Try instead
created default current_timestamp
This works:
conn.execute('''CREATE TABLE todo
(id serial primary key,
title text,
created default current_timestamp,
done boolean default 'f');''')
You are using SQLite but are specifying data types from some other database engine. SQLite accepts only INT, TEXT, REAL, NUMERIC, and NONE. Boolean is most likely being mapped to one of the number types and therefore DEFAULT 'F' is not valid syntax (although I don't think it would be valid in any version of SQL that does support BOOLEAN as a datatype, since they general use INTEGER for the underlying storage).
Rewrite the CREATE TABLE statement with SQLite datatypes and allowable default values and your code should work fine.
More details on the (somewhat unusual) SQLite type system: http://www.sqlite.org/datatype3.html
Related
This question already has answers here:
How to use variables in SQL statement in Python?
(5 answers)
Closed 2 months ago.
def update_inv_quant():
new_quant = int(input("Enter the updated quantity in stock: "))
Hello! I'm wondering how to insert a user variable into an sql statement so that a record is updated to said variable. Also, it'd be really helpful if you could also help me figure out how to print records of the database into the actual python console. Thank you!
I tried doing soemthing like ("INSERT INTO Inv(ItemName) Value {user_iname)") but i'm not surprised it didnt work
It would have been more helpful if you specified an actual database.
First method (Bad)
The usual way (which is highly discouraged as Graybeard said in the comments) is using python's f-string. You can google what it is and how to use it more in-depth.
but basically, say you have two variables user_id = 1 and user_name = 'fish', f-string turns something like f"INSERT INTO mytable(id, name) values({user_id},'{user_name}')" into the string INSERT INTO mytable(id,name) values(1,'fish').
As we mentioned before, this causes something called SQL injection. There are many good youtube videos that demonstrate what that is and why it's dangerous.
Second method
The second method is dependent on what database you are using. For example, in Psycopg2 (Driver for PostgreSQL database), the cursor.execute method uses the following syntax to pass variables cur.execute('SELECT id FROM users WHERE cookie_id = %s',(cookieid,)), notice that the variables are passed in a tuple as a second argument.
All databases use similar methods, with minor differences. For example, I believe SQLite3 uses ? instead of psycopg2's %s. That's why I said that specifying the actual database would have been more helpful.
Fetching records
I am most familiar with PostgreSQL and psycopg2, so you will have to read the docs of your database of choice.
To fetch records, you send the query with cursor.execute() like we said before, and then call cursor.fetchone() which returns a single row, or cursor.fetchall() which returns all rows in an iterable that you can directly print.
Execute didn't update the database?
Statements executing from drivers are transactional, which is a whole topic by itself that I am sure will find people on the internet who can explain it better than I can. To keep things short, for the statement to physically change the database, you call connection.commit() after cursor.execute()
So finally to answer both of your questions, read the documentation of the database's driver and look for the execute method.
This is what I do (which is for sqlite3 and would be similar for other SQL type databases):
Assuming that you have connected to the database and the table exists (otherwise you need to create the table). For the purpose of the example, i have used a table called trades.
new_quant = 1000
# insert one record (row)
command = f"""INSERT INTO trades VALUES (
'some_ticker', {new_quant}, other_values, ...
) """
cur.execute(command)
con.commit()
print('trade inserted !!')
You can then wrap the above into your function accordingly.
I work with the Python mysql.connector for the first time and I am not able to create a working insert statement.
This is the table:
'CREATE TABLE IF NOT EXISTS products (id INT AUTO_INCREMENT PRIMARY KEY, title VARCHAR(255));'
I am trying to insert a variable as title while the id should be auto incremented. I have tried multiple solutions but it simply won't work.
def insert_product(title: str):
insert_product_query = 'INSERT INTO products (title) VALUES (%s);'
cursor.execute(insert_product_query, (title,))
This runs without any error, but the insert is not working. It does nothing. I tried multiple versions of this, with '?' instead of '%s' and without a tuple but it won't work.
Another solution I tried is this:
def insert_product(title: str):
insert_product_query = f'INSERT INTO products (title) VALUES (\'{title}\')'
print(insert_product_query)
cursor.execute(insert_product_query)
I printed the insert statement and when I copy paste it directly into the database it works perfectly, so I don't have any idea why it is not working out of the python code as it is not producing any errors.
I found many similar problems but none of the solution worked for me.
I hope someone can help me as I might overlook something obvious.
Thanks in advance!
Python's connector disables autocommit by default (as a reasonable library would do!). You need to explicitly commit after you perform a DML statement:
con.commit() # Assuming con is the name of the connection variable
I had no problem with SELECTing data in python from postgres database using cursor/execute. Just changed the sql to INSERT a row but nothing is inserted to DB. Can anyone let me know what should be modified? A little confused because everything is the same except for the sql statement.
<!-- language: python -->
#app.route("/addcontact")
def addcontact():
# this connection/cursor setting showed no problem so far
conn = pg.connect(conn_str)
cur = conn.cursor(cursor_factory=psycopg2.extras.DictCursor)
sql = f"INSERT INTO jna (sid, phone, email) VALUES ('123','123','123')"
cur.execute(sql)
return redirect("/contacts")
first look at your table setup and make sure your variables are named right in the right order, format and all that, if your not logging into the specific database on the sql server it won't know where the table is, you might need to send something like 'USE databasename' before you do your insert statement so your computer is in the right place in the server.
I might not be up to date with the language but is that 'f' supposed to be right before the quotes? if thats in ur code that'd probably throw an error unless it has a use im not aware of or its not relevant to the problem.
You have to commit your transaction by adding the line below after execute(sql)
conn.commit()
Ref: Using INSERT with a PostgreSQL Database using Python
I want to use SQLAlchemy to create a view in my PostgreSQL database. I'm using the CreateView compiler from sqlalchemy-views. I'm using the answer to this question as a reference:
How to create an SQL View with SQLAlchemy?
My code for creating the view looks like this:
def create_view(self, myparameter):
mytable = Table('mytable', metadata, autoload=True)
myview = Table('myview', metadata)
engine.execute(CreateView(myview, mytable.select().where(mytable.c.mycolumn==myparameter)))
However, when I attempt to run this query, the following exception is thrown:
KeyError: 'mycolumn_1'
Looking at the compiled query, it seems that a placeholder for my parameter value is not being replaced:
'\nCREATE VIEW myview AS SELECT mytable.mycolumn \nFROM mytable \nWHERE mytable.mycolumn = %(mycolumn_1)s\n\n'
Since the placeholder is not being replaced, the query obviously fails. However, I do not understand why the replacement does not happen, since my code does not differ much from the example.
My first suspicion was that maybe the type of the parameter and the column were incompatible. Currently, the parameter comes in as a unicode string, which should be mapped to a text column in my database. I have also tried mapping the parameter as a long to a bigint column with the same (failed) result.
Does anyone have another suggestion?
From the SQLAlchemy documentation, I can see that when one wants to pass the actual value that will be ultimately used at expression time, the bindparam() is used. A nice example is also provided:
from sqlalchemy import bindparam
stmt = select([users_table]).\
where(users_table.c.name == bindparam('username'))
The following query causes python to crash ('python.exe has encountered a problem ...'
Process terminated with an exit code of -1073741819
The query is:
create temp table if not exists MM_lookup2 as
select lower(Album) || lower(SongTitle) as concat, ID
from MM.songs
where artist like '%;%' collate nocase
If I change from "like" to = it runs as expected, eg
create temp table if not exists MM_lookup2 as
select lower(Album) || lower(SongTitle) as concat, ID
from MM.songs
where artist = '%;%' collate nocase
I am running python v2.7.2, with whatever version of sqlite that ships in there.
The problem query runs without problem outside python.
You didn't write the database system/driver you are using. I suspect that your SQL is the problem. The % characters needs to be escaped. Possibly the db driver module tries to interpret %, and %) as format chars, and it cannot convert non-existing parameter value into a format that is acceptable by the database backend.
Can you please give us concrete Python code? Can you please try to run the same query but putting the value of '%,%' into a parameter, and pass it to the cursor as a parameter?