Function sequence error (0) while inserting NULL value into NULLable VARCHAR/NVARCHAR(MAX) Column

Environment

To diagnose, we usually need to know the following, including version numbers. On Windows, be sure to specify 32-bit Python or 64-bit:

• Python: 3.5.4 64-bit
• pyodbc: 4.0.24
• OS: Windows 10
• DB: SQL Server 2017
• driver: ODBC Driver 17 for SQL Server

Issue

Expected behavior: Insert NULL into nullable varchar/nvarchar(max) column with fast_executemany=True. What happens: pyodbc.Error: Function sequence error (0) (SqlParamData)

Reproduction:

CREATE TABLE TestTable
(
	LongerContent NVARCHAR(MAX) NULL,
)

Works:

sql = """
INSERT INTO TestTable (LongerContent) VALUES (?)
"""

params = (
    ('ajhdiwopwqlwdlsdlpwdlowde',), (None,),
)


con = pyodbc.connect('DRIVER={ODBC Driver 17 for SQL Server};SERVER=server;DATABASE=db;Trusted_Connection=yes;')
cursor = con.cursor()
cursor.fast_executemany=False
cursor.executemany(sql, params)
con.commit()

Results in Function sequence error (0):

import pyodbc

sql = """
INSERT INTO TestTable (LongerContent) VALUES (?)
"""

params = (
    ('ajhdiwopwqlwdlsdlpwdlowde',), (None,),
)


con = pyodbc.connect('DRIVER={ODBC Driver 17 for SQL Server};SERVER=server;DATABASE=db;Trusted_Connection=yes;')
cursor = con.cursor()
cursor.fast_executemany=True
cursor.executemany(sql, params)
con.commit()

so it seems to be a problem with the fast_executemany option.

ODBC Trace: SQL.LOG

[v-makouz]

@gizmo93 I’ve made a pull request for a fix for this error. It seems that in python 3 the parameters are not bytes, but Unicode objects and to allow them to be used by SQLPutData I need to convert them into a bytes object.

Tested on Windows 10 and Ubuntu 17.04, I also ran sqlservertests.py, mysqltests.py and pgtests.py using Python 2 and 3 and didn’t see any new errors.

https://github.com/mkleehammer/pyodbc/pull/467

@mkleehammer Let me know if you need me to make any further changes

[v-chojas]

@gordthompson Yes we are aware of the cause, and will be working on a solution to it.