Hi..while using the follwing code i am getting duplicate entries in my table..
Please suggest some method to avoid such duplicate entries..!!
Is there any other mode of INSERT query to acheive duplication free tables..???
import psycopg2
def connect():
con=psycopg2.connect("dbname='book_store' user='postgres' password='5283' host='localhost' port='5432' ")
cur=con.cursor()
cur.execute("CREATE TABLE if not exists books(id SERIAL PRIMARY KEY,title TEXT NOT NULL,author TEXT NOT NULL,year integer NOT NULL,isbn integer NOT NULL)")
con.commit()
con.close()
def insert(title,author,year,isbn):
con=psycopg2.connect("dbname='book_store' user='postgres' password='5283' host='localhost' port='5432'")
cur=con.cursor()
cur.execute("INSERT INTO books(title,author,year,isbn) VALUES(%s,%s,%s,%s)",(title,author,year,isbn))
con.commit()
con.close()
connect()
insert("the sun","helen",1997,23456777)
insert("the sun","helen",1997,23456777)
Here the same entry gets added again..where i want my code to neglect such duplication..!!!
Ideally there should be primary key or Unique key constraint defined on the table to avoid duplicates but if you want to insert only if that record doesn't exists then you can use below insert statement with select & where not exists clause
INSERT INTO books(title,author,year,isbn) select #title,#author,#year,#isbn from books where
not exists (select 1 from books where title=#title and author=#author and year=#year and isbn=#isbn);
In where condition should check for Primary OR Unique key columns instead of all the columns.
Related
The problem now is that I can only enter one record. No errors are recorded. It just takes the first record from one database and puts in the other database. I am trying to create a machine usable database from the user interface database. I will try to transfer around 100 records once it is working. I would appreciate in comments or suggestions. Thank you!
import sqlite3
sql = 'INSERT INTO heavenStream (scene, cascade, enclosure, sensor, streamer, dither) VALUES (?, ?, ?, ?, ?, ?)'
def dropTable(crs,conn):
crs.execute("DROP TABLE IF EXISTS heavenStream")
def createTable(crs,conn):
sql ='''CREATE TABLE heavenStream(
id INTEGER PRIMARY KEY AUTOINCREMENT,
scene TEXT,
cascade TEXT,
enclosure TEXT,
sensor TEXT,
streamer TEXT,
dither TEXT,
timeStream TEXT,
streamTime TEXT
)'''
crs.execute(sql)
print("Table created successfully........")
def insert_one(conn, crs):
crs.execute("SELECT * FROM animalStream")
for row in crs:
scene = row[1]
cascade = row[2]
enclosure = row[3]
sensor = row[4]
streamer = row[5]
dither = row[6]
print(f"{row[1]} {row[2]} {row[3]} {row[4]} {row[5]} {row[6]}")
try:
crs.execute(sql, (scene, cascade, enclosure,
sensor,streamer,dither))
except sqlite3.IntegrityError as err:
print('sqlite error: ', err.args[0]) # column name is
not unique
conn.commit()
def main():
conn = sqlite3.connect("/home/harry/interface/wildlife.db")
crs = conn.cursor()
dropTable(crs,conn)
createTable(crs,conn)
insert_one(conn, crs)
# conn.commit()
conn.close()
print('done')
main()
The user interface database has had records deleted. There is one record with an id of 64 and the rest are in the 90's.
The cursor (crs) changes here
crs.execute(sql, (scene, cascade, enclosure,sensor,streamer,dither))
after the first insert. Therefore, there are "no more rows to fetch" in the orginal crs.
One solution would be to instantiate another cursor for the insert. Another solution would be to fetchall() the rows into a variable and iterate over that variable as with:
rows = crs.execute("SELECT * FROM animalStream").fetchall()
for row in rows:
Using SQLite3 and got this error:
sqlite3.OperationalError: no such column: year
SQLite3 newbie over here.
Really confused right now as to what part of the code went wrong...
import sqlite3
def connect():
conn=sqlite3.connect("books.db")
cur=conn.cursor()
cur.execute("CREATE TABLE IF NOT EXISTS book (id INTEGER PRIMARY KEY, title text, author text, year integer, isbn integer)")
conn.commit()
conn.close()
def search(title="",author="",year="",isbn=""):
conn=sqlite3.connect("books.db")
cur=conn.cursor()
cur.execute("SELECT * FROM book WHERE title=? OR author=? OR year=? OR isbn=?",(title,author,year,isbn))
rows=cur.fetchall()
conn.close()
return rows
connect()
print(search(year=1918))
Any help would be appreciated, thanks!!!
Make sure that you have that column.
To list all the columns of the table book:
sqlite3 books.db
and after that:
.schema book
If you don't have a column with the name year you can add it by altering the table, or you can delete your old table and create it again.
One possibility is that no such column exists (the message is correct) because you already created the table, in an earlier version of your code which didn't have that column, so the CREATE TABLE IF NOT EXISTS silently returns.
You could very this manually by examining .schema in interactive sqlite3.
And/or you could cover the possibility in your code by checking the table structure with e.g.
SELECT * FROM sqlite_master;
If it's not correct, you could use ALTER TABLE book ADD COLUMN ... - if you wanted to rename a column, it's more complicated: SQLite Query Language: ALTER TABLE
I have been having some trouble with my understanding of how foreign keys work in sqlite3.
Im trying to get the userid (james) in one table userstuff to appear as foreign key in my otherstuff table. Yet when I query it returns None.
So far I have tried:
Enabling foreign key support
Rewriting a test script (that is being discussed here) to isolate issue
I have re-written some code after finding issues in how I had initially written it
After some research I have come across joins but I do not think this is the solution as my current query is an alternative to joins as far as I am aware
Code
import sqlite3 as sq
class DATAB:
def __init__(self):
self.conn = sq.connect("Atest.db")
self.conn.execute("pragma foreign_keys")
self.c = self.conn.cursor()
self.createtable()
self.defaultdata()
self.show_details() # NOTE DEFAULT DATA ALREADY RAN
def createtable(self):
self.c.execute("CREATE TABLE IF NOT EXISTS userstuff("
"userid TEXT NOT NULL PRIMARY KEY,"
" password TEXT)")
self.c.execute("CREATE TABLE IF NOT EXISTS otherstuff("
"anotherid TEXT NOT NULL PRIMARY KEY,"
"password TEXT,"
"user_id TEXT REFERENCES userstuff(userid))")
def defaultdata(self):
self.c.execute("INSERT INTO userstuff (userid, password) VALUES (?, ?)", ('james', 'password'))
self.c.execute("INSERT INTO otherstuff (anotherid, password, user_id) VALUES (?, ?, ?)",('aname', 'password', 'james'))
self.conn.commit()
def show_details(self):
self.c.execute("SELECT user_id FROM otherstuff, userstuff WHERE userstuff.userid=james AND userstuff.userid=otherstuff.user_id")
print(self.c.fetchall())
self.conn.commit()
-----NOTE CODE BELOW THIS IS FROM NEW FILE---------
import test2 as ts
x = ts.DATAB()
Many thanks
A foreign key constraint is just that, a constraint.
This means that it prevents you from inserting data that would violate the constraint; in this case, it would prevent you from inserting a non-NULL user_id value that does not exist in the parent table.
By default, foreign key constraints allow NULL values. If you want to prevent userstuff rows without a parent row, add a NOT NULL constraint to the user_id column.
In any case, a constraint does not magically generate data (and the database cannot know which ID you want). If you want to reference a specific row of the parent table, you have to insert its ID.
I have to code on python sqlite3 a function to count rows of a table.
The thing is that the user should input the name of that table once the function is executed.
So far I have the following. However, I don't know how to "connect" the variable (table) with the function, once it's executed.
Any help would be great.
Thanks
def RT():
import sqlite3
conn= sqlite3.connect ("MyDB.db")
table=input("enter table name: ")
cur = conn.cursor()
cur.execute("Select count(*) from ?", [table])
for row in cur:
print str(row[0])
conn.close()
Columns and Tables Can't be Parameterized
As explained in this SO answer, Columns and tables can't be parameterized. A fact that might not be documented by any authoritative source (I couldn't find one, so if you you know of one please edit this answer and/or the one linked above), but instead has been learned through people trying exactly what was attempted in the question.
The only way to dynamically insert a column or table name is through standard python string formatting:
cur.execute("Select count(*) from {0}".format(table))
Unfortunately This opens you up to the possibility of SQL injection
Whitelist Acceptable Column/Table Names
This SO answer explains that you should use a whitelist to check against acceptable table names. This is what it would look like for you:
import sqlite3
def RT():
conn = sqlite3.connect ("MyDB.db")
table = input("enter table name: ")
cur = conn.cursor()
if table not in ['user', 'blog', 'comment', ...]:
raise ... #Include your own error here
execute("Select count(*) from {0}".format(table))
for row in cur:
print str(row[0])
conn.close()
The same SO answer cautions accepting submitted names directly "because the validation and the actual table could go out of sync, or you could forget the check." Meaning, you should only derive the name of the table yourself. You could do this by making a clear distinction between accepting user input and the actual query. Here is an example of what you might do.
import sqlite3
acceptable_table_names = ['user', 'blog', 'comment', ...]
def RT():
"""
Client side logic: Prompt the user to enter table name.
You could also give a list of names that you associate with ids
"""
table = input("enter table name: ")
if table in acceptable_table_names:
table_index = table_names.index(table)
RT_index(table_index)
def RT_index(table_index):
"""
Backend logic: Accept table index instead of querying user for
table name.
"""
conn = sqlite3.connect ("MyDB.db")
cur = conn.cursor()
table = acceptable_table_names[table_index]
execute("Select count(*) from {0}".format(table))
for row in cur:
print str(row[0])
conn.close()
This may seem frivolous, but this keeps the original interface while addressing the potential problem of forgetting to check against a whitelist. The validation and the actual table could still go out of sync; you'll need to write tests to fight against that.
I have a sqlite3 table as shown below
Record(WordID INTEGER PRIMARY KEY, Word TEXT, Wordcount INTEGER, Docfrequency REAL).
I want to create and insert data into this table if the table not exists else I want to update the table in such a way that only 'Wordcount' column get updated on the basis(Reference) of data in the column 'Word'. I am trying to execute this from a python program like
import sqlite3
conn = sqlite3.connect("mydatabase")
c = conn.cursor()
#Create table
c.execute("CREATE TABLE IF NOT EXISTS Record(WordID INTEGER PRIMARY KEY, Words TEXT, Wordcount INTEGER, Docfrequency REAL)")
#Update table
c.execute("UPDATE TABLE IF EXISTS Record")
#Insert a row of data
c.execute("INSERT INTO Record values (1,'wait', 9, 10.0)")
c.execute("INSERT INTO Record values (2,'Hai', 5, 6.0)")
#Updating data
c.execute("UPDATE Record SET Wordcount='%d' WHERE Words='%s'" %(11,'wait') )
But I can't update the table. On running the program I am getting the error message as
c.execute("UPDATE TABLE IF EXISTS Record")
sqlite3.OperationalError: near "TABLE": syntax error
How should I write the code to update the table ?
Your SQL query for UPDATE is invalid - see the documentation.
Also, I don't understand why you'd want to check for the table's existence when updating, given that just before that you're creating it if it doesn't exist.
If your goal is to update an entry if it exists or insert it if it doesn't, you might do it either by:
First doing an UPDATE and checking the number of rows updated. If 0, you know the record didn't exist and you should INSERT instead.
First doing an INSERT - if there's an error related to constraint violation, you know the entry already existed and you should do an UPDATE instead.