Binding list to params in Pandas read_sql_query with other params

Question

I've been trying to test various methods for making my code to run. To begin with, I have this list:

member_list = [111,222,333,444,555,...]

I tried to pass it into this query:

query = pd.read_sql_query(
"""
select member id
    ,yearmonth
from queried_table
where yearmonth between ? and ?
    and member_id in ?
""", db2conn, params = [201601, 201603, member_list])

However, I get an error that says:

'Invalid parameter type. param-index=2 param-type=list', 'HY105'

So I looked around and tried using formatted strings:

query = pd.read_sql_query(
"""
select member id
    ,yearmonth
from queried_table
where yearmonth between ? and ?
    and member_id in (%s)
""" % ','.join(['?']*len(member_list), db2conn, params = [201601, 201603, tuple(member_list)])

Now, I get the error:

'The SQL contains 18622 parameter markers, but 3 parameters were supplied', 'HY000'

because it's looking to fill in all the ? placeholders in the formatted string.

So, ultimately, is there a way to somehow evaluate the list and pass each individual element to bind to the ? or is there another method I could use to get this to work?

Btw, I'm using pyodbc as my connector.

Thanks in advance!

Answer 1

Break this up into three parts to help isolate the problem and improve readability:

1. Build the SQL string
2. Set parameter values
3. Execute pandas.read_sql_query

---

Build SQL

First ensure ? placeholders are being set correctly. Use str.format with str.join and len to dynamically fill in ?s based on member_list length. Below examples assume 3 member_list elements.

Example

member_list = (1,2,3)
sql = """select member_id, yearmonth
         from queried_table
         where yearmonth between {0} and {0}
         and member_id in ({1})"""
sql = sql.format('?', ','.join('?' * len(member_list)))
print(sql)

Returns

select member_id, yearmonth
from queried_table
where yearmonth between ? and ?
and member_id in (?,?,?)

---

Set Parameter Values

Now ensure parameter values are organized into a flat tuple

Example

# generator to flatten values of irregular nested sequences,
# modified from answers http://stackoverflow.com/questions/952914/making-a-flat-list-out-of-list-of-lists-in-python
def flatten(l):
    for el in l:
        try:
            yield from flatten(el)
        except TypeError:
            yield el

params = tuple(flatten((201601, 201603, member_list)))
print(params)

Returns

(201601, 201603, 1, 2, 3)

---

Execute

Finally bring the sql and params values together in the read_sql_query call

query = pd.read_sql_query(sql, db2conn, params)