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Alter query according to user selection in sqlite python

I have a sqlite database named StudentDB which has 3 columns Roll number, Name, Marks. Now I want to fetch only the columns that user selects in the IDE. User can select one column or two or all the three. How can I alter the query accordingly using Python?
I tried:
import sqlite3
sel={"Roll Number":12}
query = 'select * from StudentDB Where({seq})'.format(seq=','.join(['?']*len(sel))),[i for k,i in sel.items()]
con = sqlite3.connect(database)
cur = con.cursor()
cur.execute(query)
all_data = cur.fetchall()
all_data
I am getting:
operation parameter must be str

You should control the text of the query. The where clause shall allways be in the form WHERE colname=value [AND colname2=...] or (better) WHERE colname=? [AND ...] if you want to build a parameterized query.
So you want:
query = 'select * from StudentDB Where ' + ' AND '.join('"{}"=?'.format(col)
for col in sel.keys())
...
cur.execute(query, tuple(sel.values()))

In your code, the query is now a tuple instead of str and that is why the error.
I assume you want to execute a query like below -
select * from StudentDB Where "Roll number"=?
Then you can change the sql query like this (assuming you want and and not or) -
query = "select * from StudentDB Where {seq}".format(seq=" and ".join('"{}"=?'.format(k) for k in sel.keys()))
and execute the query like -
cur.execute(query, tuple(sel.values()))
Please make sure in your code the provided database is defined and contains the database name and studentDB is indeed the table name and not database name.

Python MySQL query using string comparison in where clause

I have a strange issue where I can't get an SQL query with parameter to work with a string comparison in the where clause - I don't get a row back. when i connect to the MySQL db via bash, the query works.
python 3.7.3
mysql-connector-python==8.0.11
mysql 5.7
works (getting my row):
select * from my_table where my_column = 'my_string';
also works (getting my row):
cursor.execute(
"""
select *
from my_table
where my_column = 'my_string'
"""
)
doesn't work (cursor.fetchall() is []):
cursor.execute(
"""
select *
from my_table
where my_column = '%s'
""",
('my_string')
)

Be careful with tuples. I think you need ('my_string',).
FYI I wrote the original comment mentioned by #tscherg in his comment below the question.

Remove the quotes:
cursor.execute(
"""
select *
from my_table
where my_column = %s
""",
('my_string')
)

how to using MySQL pattern matching and binding parameters in sql query in python?

I know how to use MySQL pattern matching, for example:
SELECT * FROM table WHERE col LIKE '%mid%'
I also know how to bind parameters into a sql query in python, for example:
import MySQLdb
s = 'something'
db = MySQLdb.connect(host=blablabla...)
cur = db.cursor()
sql = "SELECT * FROM table WHERE col = %s"
cur.execute(sql, s)
data = cur.fetchall()
db.close()
But I can't find a method to combine these together in one query, like
sql = "SELECT * FROM table WHERE col LIKE '%%s%'"
cur.execute(sql, s)
where the first and the third '%' are pattern character and the middle '%s' is used to bind parameter s.
Anyone have an idea?

Alright, I will answer myself..
#dsgdfg inspired me and here is my code:
sql = "SELECT * FROM table WHERE col LIKE %s"
cur.execute(sql, "%"+s+"%")

sql = "SELECT * FROM table WHERE col LIKE CONCAT('%', %s, '%')"
cur.execute(sql, s)
(I am assuming that execute deals with escaping, thereby preventing SQL injection.)

for the people using py charm
you can do this
qq=input("enter the author name:")
print(pd.read_sql_query("select Book_Id,Book_Name,book_author from bookd where book_author like '%s'" %("%"+qq+"%",), conn2))

Return all values when a condition value is NULL

Suppose I have the following very simple query:
query = 'SELECT * FROM table1 WHERE id = %s'
And I'm calling it from a python sql wrapper, in this case psycopg:
cur.execute(query, (row_id))
The thing is that if row_id is None, I would like to get all the rows, but that query would return an empty table instead.
The easy way to approach this would be:
if row_id:
cur.execute(query, (row_id))
else:
cur.execute("SELECT * FROM table1")
Of course this is non idiomatic and gets unnecessarily complex with non-trivial queries. I guess there is a way to handle this in the SQL itself but couldn't find anything. What is the right way?

Try to use COALESCE function as below
query = 'SELECT * FROM table1 WHERE id = COALESCE(%s,id)'

SELECT * FROM table1 WHERE id = %s OR %s IS NULL
But depending how the variable is forwarded to the query it might be better to make it 0 if it is None
SELECT * FROM table1 WHERE id = %s OR %s = 0

Python MySQL executemany in WHERE clause

I want to select values from MySQL as follows
do_not_select = [1,2,3]
cursor = database.cursor()
cursor.executemany("""SELECT * FROM table_a WHERE id != %s""",(do_not_select))
data = cursor.fetchall()
The query return all the values in the db apart form the first id (1). I don't want it to select id 1,2 or 3 however.
Is this possible using the executemany command..?

Give NOT IN a go:
do_not_select = [1, 2, 3]
cursor.execute("""SELECT * FROM table_a
WHERE id NOT IN ({}, {}, {})""".format(do_not_select[0],
do_not_select[1],
do_not_select[2]))
data.cursor.fetchall()
I suspect (though I haven't tested this) that this would work better id do_not_select was a tuple, then I think you could just fire it straight into your query:
do_not_select = (1, 2, 3)
cursor.execute("""SELECT * FROM table_a
WHERE id NOT IN {}""".format(do_not_select))
data.cursor.fetchall()
I'd be interested to know if this works - if you try it please let me know :)