creating a pandas dataframe from a database query that uses bind variables

问题

I'm working with an Oracle database. I can do this much:

    import pandas as pd
    import pandas.io.sql as psql
    import cx_Oracle as odb
    conn = odb.connect(_user +'/'+ _pass +'@'+ _dbenv)

    sqlStr = "SELECT * FROM customers"
    df = psql.frame_query(sqlStr, conn)

But I don't know how to handle bind variables, like so:

    sqlStr = """SELECT * FROM customers 
                WHERE id BETWEEN :v1 AND :v2
             """

I've tried these variations:

   params  = (1234, 5678)
   params2 = {"v1":1234, "v2":5678}

   df = psql.frame_query((sqlStr,params), conn)
   df = psql.frame_query((sqlStr,params2), conn)
   df = psql.frame_query(sqlStr,params, conn)
   df = psql.frame_query(sqlStr,params2, conn)

The following works:

   curs = conn.cursor()
   curs.execute(sqlStr, params)
   df = pd.DataFrame(curs.fetchall())
   df.columns = [rec[0] for rec in curs.description]

but this solution is just...inellegant. If I can, I'd like to do this without creating the cursor object. Is there a way to do the whole thing using just pandas?

回答1:

Try using pandas.io.sql.read_sql_query. I used pandas version 0.20.1, I used it, it worked out:

import pandas as pd
import pandas.io.sql as psql
import cx_Oracle as odb
conn = odb.connect(_user +'/'+ _pass +'@'+ _dbenv)

sqlStr = """SELECT * FROM customers 
            WHERE id BETWEEN :v1 AND :v2
"""
pars = {"v1":1234, "v2":5678}
df = psql.frame_query(sqlStr, conn, params=pars)

回答2:

As far as I can tell, pandas expects that the SQL string be completely formed prior to passing it along. With that in mind, I would (and always do) use string interpolation:

params = (1234, 5678)
sqlStr = """
SELECT * FROM customers 
WHERE id BETWEEN %d AND %d
""" % params
print(sqlStr)

which gives

SELECT * FROM customers 
WHERE id BETWEEN 1234 AND 5678

So that should feed into psql.frame_query just fine. (it does in my experience with postgres, mysql, and sql server).

来源：https://stackoverflow.com/questions/14884686/creating-a-pandas-dataframe-from-a-database-query-that-uses-bind-variables

标签

python

sql

database

Oracle

pandas