如何判断sqlite3数据库中是否存在值，python[duplicate]

Question

如何判断sqlite3数据库中是否存在值，python

以下是我目前的代码：

def signup():
    email = request.form['email']
    username = request.form['user']
    password = request.form['password']
    g.db.execute("INSERT INTO users VALUES (?, ?, ?)", [email, username, password])
    g.db.commit()

如果数据库中没有电子邮件和用户名，我希望它只将值插入数据库，但我不知道从哪里开始。

Answer 1

您所要做的就是在插入之前进行查询，然后执行fetchone。如果fetchone返回一些信息，那么您可以确定数据库中已经有一条记录包含电子邮件或用户名：

def signup():
    email = request.form['email']
    username = request.form['user']
    password = request.form['password']

    # Create cursor object
    cur = g.db.cursor()

    # run a select query against the table to see if any record exists
    # that has the email or username
    cur.execute("""SELECT email
                          ,username
                   FROM users
                   WHERE email=?
                       OR username=?""",
                (email, username))

    # Fetch one result from the query because it
    # doesn't matter how many records are returned.
    # If it returns just one result, then you know
    # that a record already exists in the table.
    # If no results are pulled from the query, then
    # fetchone will return None.
    result = cur.fetchone()

    if result:
        # Record already exists
        # Do something that tells the user that email/user handle already exists
    else:
        cur.execute("INSERT INTO users VALUES (?, ?, ?)", (email, username, password))
        g.db.commit()