有没有一种方法可以在Python中动态使用SQLite IN
命令,而不提供准确的占位符数
例如,假设我正在尝试:
SELECT
*
FROM mytable
WHERE somecol IN (1, 3, 4, 7, 9)
在Python中,占位符是长度至少为1的元组,但我不确定如何(或者甚至,如果有可能)将它们与IN
命令一起使用。我尝试过纯元组、字符串元组和纯字符串,包括自由元组和封闭元组,但均无效:
In [1]: import sqlite3
...: conn = sqlite3.connect(':memory:')
...: cur = conn.cursor()
...: l = [(i, chr(i+64)) for i in range(1, 11)]
...: cur.execute('CREATE TABLE mytable (somecol INTEGER, char TEXT)')
...: cur.executemany('INSERT INTO mytable VALUES(?, ?)', l)
...: conn.commit()
In [2]: tup = ((1, 3, 4, 7, 9),)
...: cur.execute('SELECT * FROM mytable WHERE somecol IN ?', tup)
OperationalError Traceback (most recent call last)
<ipython-input-2-195e99af7b4f> in <module>
----> 1 cur.execute('SELECT * FROM mytable WHERE somecol IN ?', tup).fetchall()
OperationalError: near "?": syntax error
In [3]: cur.execute('SELECT * FROM mytable WHERE somecol IN (?)', tup).fetchall()
---------------------------------------------------------------------------
InterfaceError Traceback (most recent call last)
<ipython-input-2-a6c2d28cce18> in <module>
----> 1 cur.execute('SELECT * FROM mytable WHERE somecol IN (?)', tup).fetchall()
InterfaceError: Error binding parameter 0 - probably unsupported type.
In [4]: tups = tuple(str(i) for i in tup)
...: cur.execute('SELECT * FROM mytable WHERE somecol IN ?', tups)
OperationalError Traceback (most recent call last)
<ipython-input-3-195e99af7b4f> in <module>
----> 1 cur.execute('SELECT * FROM mytable WHERE somecol IN ?', tups).fetchall()
OperationalError: near "?": syntax error
In [5]: # Empty list due to trying to fetch a somecol string value of "(1, 3, 4, 7, 9)"
...: cur.execute('SELECT * FROM mytable WHERE somecol IN (?)', tups).fetchall()
Out[5]: []
In [6]: stup = (', '.join(str(i) for i in tup[0]),)
...: cur.execute('SELECT * FROM mytable WHERE somecol IN ?', stup)
OperationalError Traceback (most recent call last)
<ipython-input-5-195e99af7b4f> in <module>
----> 1 cur.execute('SELECT * FROM mytable WHERE somecol IN ?', stup).fetchall()
OperationalError: near "?": syntax error
In [7]: # Empty list due to trying to fetch a somecol string value of "1, 3, 4, 7, 9"
...: cur.execute('SELECT * FROM mytable WHERE somecol IN (?)', stup).fetchall()
Out[7]: []
我知道如果我提供cur.execute('SELECT * FROM mytable WHERE somecol IN (?, ?, ?, ?, ?)', tup[0]).fetchall()
,我会得到想要的结果,但那是因为我事先知道tup[0]
的长度,并相应地调整了光标。然而,这将在我无法预料的应用程序上出现故障
我几乎可以肯定,在Python中,这实际上不是feasbile,但我想知道为什么是这样,为什么应该是这样
由于参数列表不能具有相同的长度,因此必须使用字符串格式来生成正确数量的参数标记检查此答案here
sqlite不支持其他数据库支持的序列占位符
为了解决这个问题,您只需在一个序列中根据需要生成尽可能多的单个占位符。类似Via:
'(' + ','.join('?'*len(v)) + ')'
可以以逗号分隔的字符串连接所有值:
然后使用运算符
LIKE
而不是IN
:这样,您只需要一个占位符
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