python mysql ValueError：无法处理参数

Question

I have some python code that adds a column to a table and then iterates through a list and adds each value to the column. It adds the column, but it does not add any of the values. It gives me the error ValueError: Could not process parameters, but when I type the same commands into the mysql console then it works just fine. Below is the relevant portion of my code and the error message. Let me know if there is anything obviously wrong. please and thankyou.

mycursor = mydb.cursor()
colname=input()
que="ALTER TABLE timestamps ADD {} TIMESTAMP(6) ".format(colname)
mycursor.execute(que)
print(que)
for i in range(len(res)):    
    val = res[i]
    print(val)
    sql = "INSERT INTO timestamps ({}) VALUES ('{}') ".format(colname,val)
    print(sql)
    mycursor.execute(sql, val)
mydb.commit()

asdf
ALTER TABLE timestamps ADD asdf TIMESTAMP(6) 
2021-05-23 02:32:20.660
INSERT INTO timestamps (asdf) VALUES ('2021-05-23 02:32:20.660') 
Traceback (most recent call last):
  File "upload_onsets.py", line 89, in <module>
    mycursor.execute(sql, val)
  File "/home/ubuntu2004/.local/lib/python3.8/site-packages/mysql/connector/cursor_cext.py", line 257, in execute
    prepared = self._cnx.prepare_for_mysql(params)
  File "/home/ubuntu2004/.local/lib/python3.8/site-packages/mysql/connector/connection_cext.py", line 651, in prepare_for_mysql
    raise ValueError("Could not process parameters")
ValueError: Could not process parameters

Answer 1

Since you're providing the value in the cursor.execute() , you need to put a placeholder into the SQL, not format the value into it.

And the second argument to cursor.execute() should be a tuple, not a single value.

There's no need to assign sql inside the loop, since it doesn't change.

sql = "INSERT INTO timestamps ({}) VALUES (%s) ".format(colname)
print(sql)
for i in range(len(res)):    
    val = res[i]
    print(val)
    mycursor.execute(sql, (val,))

However, you can do this more efficiently using executemany() instead of a loop.

sql = "INSERT INTO timestamps ({}) VALUES (%s) ".format(colname)
vals = [(val,) for val in res]
mycursor.executemany(sql, vals)

This will combine all the inserts into a single query with multiple VALUES lists.