Develop Reference

Illegal Variable Name/Number when Passing in Python List

I'm trying to run SQL statements through Python on a list.
By passing in a list, in this case date. Since i want to run multiple SELECT SQL queries and return them.
I've tested this by passing in integers, however when trying to pass in a date I am getting ORA-01036 error. Illegal variable name/number. I'm using an Oracle DB.
cursor = connection.cursor()
date = ["'01-DEC-21'", "'02-DEC-21'"]
sql = "select * from table1 where datestamp = :date"
for item in date:
cursor.execute(sql,id=item)
res=cursor.fetchall()
print(res)
Any suggestions to make this run?

You can't name a bind variable date, it's an illegal name. Also your named variable in cursor.execute should match the bind variable name. Try something like:
sql = "select * from table1 where datestamp = :date_input"
for item in date:
cursor.execute(sql,date_input=item)
res=cursor.fetchall()
print(res)

Some recommendation and warnings to your approach:
you should not depend on your default NLS date setting, while binding a String (e.g. "'01-DEC-21'") to a DATE column. (You probably need also remone one of the quotes).
You should ommit to fetch data in a loop if you can fetch them in one query (using an IN list)
use prepared statement
Example
date = ['01-DEC-21', '02-DEC-21']
This generates the query that uses bind variables for your input list
in_list = ','.join([f" TO_DATE(:d{ind},'DD-MON-RR','NLS_DATE_LANGUAGE = American')" for ind, d in enumerate(date)])
sql_query = "select * from table1 where datestamp in ( " + in_list + " )"
The sql_query generate is
select * from table1 where datestamp in
( TO_DATE(:d0,'DD-MON-RR','NLS_DATE_LANGUAGE = American'), TO_DATE(:d1,'DD-MON-RR','NLS_DATE_LANGUAGE = American') )
Note that the INlist contains one bind variable for each member of your input list.
Note also the usage of to_date with explicite mask and fixing the language to avoid problems with interpretation of the month abbreviation. (e.g. ORA-01843: not a valid month)
Now you can use the query to fetch the data in one pass
cur.prepare(sql_query)
cur.execute(None, date)
res = cur.fetchall()

Pass Column Names into SQL statement in dynamic way - Python- SQL Server

query = ('SELECT ? from table', fields)
Example of 'fields' value = name, surname, date
I can put 'fields' in a list but I do not know how many (?) to put inside the query. Because, fields variable will include sometimes 5, sometimes 10 column names. I am trying to pass column names dynamically to the query.
How can I solve this problem?

A statement could be formed like so. Values will be like "(?, ?, ?, ?)" depending on the length of fields.
# create a comma separated list of question marks
# then surround with parenthesis
values = '('+', '.join(['?']*len(fields))+')'
query=('SELECT '+values+' from table',fields)
Not saying that this will work since you didn't share specifics of how you are connecting to or querying SQL Server.
Instead you could use the join str method:
table_name = 'MyTable'
fields = ['col1','col2','col3']
values = ', '.join(fields)
statement = 'SELECT '+values+' from '+table_name
query
'SELECT col1, col2, col3 from MyTable'
query=(statement)

Concatenate the query string
str1 = "SELECT "
for fieldname in fields:
str1 = str1 + fieldname + ", "
select_query_string = str1[0:-2] + " from " +table
and then use that in query
query=(select_query_string)

Pass list values to MySQL query using Python

I want to pass list values along with other parameter values. following is my scenario. I want to pass multiple values for column "Code" and want to pass single value to "Continent" column.
param = [('AFG', 'IND'),'Asia']
query = "select * from country where Code in (%s) AND Continent = %s"
cursor.execute(query,param)
while executing in Python, I am getting following error.
Failed to execute Query: Failed processing format-parameters; Python
'tuple' cannot be converted to a MySQL type

The trick here is the WHERE IN clause, which isn't really amenable to being parameterized. One option generates an IN clause with the exact number of placeholders in your list:
codes = ('AFG', 'IND')
continent = 'Asia'
params = codes + (continent,)
where_in = ','.join(['%s'] * len(codes))
sql = "SELECT * FROM country WHERE Code IN (%s) AND Continent = %s" % (where_in, '%s')
cursor.execute(sql, params)
To see what the above script actually did, lets look at the various parts:
print(where_in)
print(sql)
%s,%s
SELECT * FROM country WHERE Code IN (%s,%s) AND Continent = %s
The trick here is that we actually use a %s placeholder twice, once for the Python string, and a second time for the SQL query string. Also, we bind a single level tuple containing all bound values:
('AFG', 'IND', 'ASIA')

first you split the list and then you split the tuple.
param = [('AFG', 'IND'),'Asia']
p1,p2=param[0]
query = "select * from country where Code in ('%s','%s') AND Continent = %s" % (p1,p2,param[1])
cursor.execute(query)

Oracle Parameters used multiple places in query

I'm trying to pass the same parameters to an oracle query in two separate places in the SQL code.
My code works if I hard code the criteria for table2 like this:
# define parameters
years = ['2018','2019']
placeholder= ':d'
placeholders= ', '.join(placeholder for unused in years)
placeholders
# create cursor
cursor = connection.cursor()
# query
qry = """
select * from table1
INNER
JOIN table2
ON table1_id = table2_id
where table1_year in (%s)
and table2_year in ['2018','2019'] --here's where I say I'm hard coding criteria
""" % placeholders
data = cursor.execute(qry, years)
df = pd.DataFrame(data.fetchall(), columns = [column[0] for column in cursor.description])
# close database connection
connection.close()
If I try to use the parameter for table2 like this:
qry = """
select * from table1
INNER
JOIN table2
ON table1_id = table2_id
where table1_year in (%s)
and table2_year in (%s) --part of code I'm having issues with
""" % placeholders
I get the following error:
TypeError: not enough arguments for format string
I can't simply rewrite the SQL because I frequently have to use someone else's code and it wouldn't be feasible to rewrite all of it.

If you want to fill multiple placeholders, you have to supply the same number of parameters.
"one meal: %s" % "sandwich" # works
"two meals: %s, %s" % "sandwich" # not working
"two meals: %s, %s" % ("sandwich", "sandwich") # works
NOTE: It is a bad/dangerous thing to use string formatting for the assembly of SQL queries (lookup "SQL Injection"). In your case it is fine, but in general you should use parameterized queries, especially when dealing with input from untrusted sources like user input. You don't want a user to input "2018; DROP TABLE table1;".

Python Sqlite3 insert operation with a list of column names

Normally, if i want to insert values into a table, i will do something like this (assuming that i know which columns that the values i want to insert belong to):
conn = sqlite3.connect('mydatabase.db')
conn.execute("INSERT INTO MYTABLE (ID,COLUMN1,COLUMN2)\
VALUES(?,?,?)",[myid,value1,value2])
But now i have a list of columns (the length of list may vary) and a list of values for each columns in the list.
For example, if i have a table with 10 columns (Namely, column1, column2...,column10 etc). I have a list of columns that i want to update.Let's say [column3,column4]. And i have a list of values for those columns. [value for column3,value for column4].
How do i insert the values in the list to the individual columns that each belong?

As far as I know the parameter list in conn.execute works only for values, so we have to use string formatting like this:
import sqlite3
conn = sqlite3.connect(':memory:')
conn.execute('CREATE TABLE t (a integer, b integer, c integer)')
col_names = ['a', 'b', 'c']
values = [0, 1, 2]
conn.execute('INSERT INTO t (%s, %s, %s) values(?,?,?)'%tuple(col_names), values)
Please notice this is a very bad attempt since strings passed to the database shall always be checked for injection attack. However you could pass the list of column names to some injection function before insertion.
EDITED:
For variables with various length you could try something like
exec_text = 'INSERT INTO t (' + ','.join(col_names) +') values(' + ','.join(['?'] * len(values)) + ')'
conn.exec(exec_text, values)
# as long as len(col_names) == len(values)

Of course string formatting will work, you just need to be a bit cleverer about it.
col_names = ','.join(col_list)
col_spaces = ','.join(['?'] * len(col_list))
sql = 'INSERT INTO t (%s) values(%s)' % (col_list, col_spaces)
conn.execute(sql, values)

I was looking for a solution to create columns based on a list of unknown / variable length and found this question. However, I managed to find a nicer solution (for me anyway), that's also a bit more modern, so thought I'd include it in case it helps someone:
import sqlite3
def create_sql_db(my_list):
file = 'my_sql.db'
table_name = 'table_1'
init_col = 'id'
col_type = 'TEXT'
conn = sqlite3.connect(file)
c = conn.cursor()
# CREATE TABLE (IF IT DOESN'T ALREADY EXIST)
c.execute('CREATE TABLE IF NOT EXISTS {tn} ({nf} {ft})'.format(
tn=table_name, nf=init_col, ft=col_type))
# CREATE A COLUMN FOR EACH ITEM IN THE LIST
for new_column in my_list:
c.execute('ALTER TABLE {tn} ADD COLUMN "{cn}" {ct}'.format(
tn=table_name, cn=new_column, ct=col_type))
conn.close()
my_list = ["Col1", "Col2", "Col3"]
create_sql_db(my_list)
All my data is of the type text, so I just have a single variable "col_type" - but you could for example feed in a list of tuples (or a tuple of tuples, if that's what you're into):
my_other_list = [("ColA", "TEXT"), ("ColB", "INTEGER"), ("ColC", "BLOB")]
and change the CREATE A COLUMN step to:
for tupl in my_other_list:
new_column = tupl[0] # "ColA", "ColB", "ColC"
col_type = tupl[1] # "TEXT", "INTEGER", "BLOB"
c.execute('ALTER TABLE {tn} ADD COLUMN "{cn}" {ct}'.format(
tn=table_name, cn=new_column, ct=col_type))

As a noob, I can't comment on the very succinct, updated solution #ron_g offered. While testing, though I had to frequently delete the sample database itself, so for any other noobs using this to test, I would advise adding in:
c.execute('DROP TABLE IF EXISTS {tn}'.format(
tn=table_name))
Prior the the 'CREATE TABLE ...' portion.
It appears there are multiple instances of
.format(
tn=table_name ....)
in both 'CREATE TABLE ...' and 'ALTER TABLE ...' so trying to figure out if it's possible to create a single instance (similar to, or including in, the def section).