input: Write a python function to read data from a CSV file and insert it into an SQLite database.
  assert main('test1.csv')==None
  assert main('test2.csv')==None
  assert main('test3.csv')==None
output: import sqlite3
  import csv
  
  def main(csv_file):
      conn = sqlite3.connect(':memory:')
      c = conn.cursor()
      
      c.execute('''
      CREATE TABLE data (
          id INTEGER PRIMARY KEY,
          column1 TEXT,
          column2 TEXT,
          column3 TEXT
      )
      ''')
      
      with open(csv_file, 'r') as f:
          reader = csv.reader(f)
          next(reader)  # Skip the header row
          for row in reader:
              c.execute('INSERT INTO data (column1, column2, column3) VALUES (?, ?, ?)', (row[0], row[1], row[2]))
      
      conn.commit()
      conn.close()