Question

有人可以告诉我为什么下面的代码会抛出错误。它的目的是查看当前的id，如果它的最小值下降到数据库中的下一行并打印它。

def loadData(self):
    connection = sqlite3.connect('films.db')
    c = connection.cursor()
    maxid_before = c.execute("SELECT * FROM FILMS WHERE ID = (SELECT MAX(ID) FROM FILMS)")
    last_row = maxid_before.fetchone()[0]
    maxid_after = c.execute("SELECT * FROM FILMS WHERE ID < (last_row) ORDER BY ID DESC LIMIT 1;").fetchone()
    print(maxid_after)

更新这是调用loadData的函数。这次我做了什么傻事。你可以忽略前5行左右。

def __init__(self):
    QtGui.QMainWindow.__init__(self)
    Ui_MainWindow.__init__(self)
    self.setupUi(self)
    self.edit_btn.clicked.connect(self.Retrieve)
    self.edit_save_btn.clicked.connect(self.insertData)
    last_id = 0
    if not last_id:
        connection = sqlite3.connect('films.db')
        c = connection.cursor()
        result = c.execute("SELECT * FROM FILMS WHERE ID = (SELECT MAX(ID) FROM FILMS)")
        last_id = result.fetchone()[0]
    self.edit_load_btn.clicked.connect(self.loadData)

这是loadData函数

def loadData(self, last_id):
    connection = sqlite3.connect('films.db')
    c = connection.cursor()
    maxid_after = c.execute("SELECT * FROM FILMS WHERE ID < ? ORDER BY ID DESC LIMIT 1;", (last_id,)).fetchone()
    print(maxid_after)
    return maxid_after

Answer 1

试试这个 -

maxid_after = c.execute("SELECT * FROM FILMS WHERE ID < ? ORDER BY ID DESC LIMIT 1;", (last_row,)).fetchone()

在您的代码last_row中，变量不是列名。因此，您应该将last_row的值放在查询中。

如果您像查询一样将last_row放在查询中，sqlite会将last_row视为列名并尝试执行此类查询。由于它无法通过该名称找到任何列，因此会抛出错误。

如果你想在按钮上运行这个功能，并在每次点击按钮时按降序逐行返回，那么你的功能应该是这样的 -

def loadData(self):
    connection = sqlite3.connect('films.db')
    c = connection.cursor()
    result = c.execute("SELECT * FROM FILMS WHERE ID < ? ORDER BY ID DESC LIMIT 1;", (last_id,)).fetchone()
    if result:
        self.last_id = result[0]
    connection.close()

调用loadData()的函数应该像 -

# This is the code that calls loadData()
# This is __init__

result = c.execute("SELECT * FROM FILMS WHERE ID = (SELECT MAX(ID) FROM FILMS)").fetchone()

if result:
    self.last_id = result[0]

...
# On button click
# Call loadData

在MAX ID Sqlite3中使用DESC - Python

1 个答案: