“SELECT ... WHERE ... IN”，参数数量未知

Question

我正在尝试以...的形式执行查询

SELECT col2 FROM tab WHERE col1 IN (val1, val2, val3...)

...值存储在任意长度的 Python 列表/元组中。我似乎找不到“干净”的方法。

>>> db = connect(":memory:")
>>> db.execute("CREATE TABLE tab (col1 INTEGER, col2 TEXT)")
>>> db.execute("INSERT INTO tab VALUES(1,'one')")
>>> db.execute("INSERT INTO tab VALUES(2,'two')")
>>> db.execute("INSERT INTO tab VALUES(3,'three')")
>>> db.execute("INSERT INTO tab VALUES(4,'four')")
>>> db.execute("INSERT INTO tab VALUES(5,'five')")
>>> db.commit()

# Expected result
>>> db.execute("SELECT col2 FROM tab WHERE col1 IN (1,3,4)").fetchall()
[(u'one',), (u'three',), (u'four',)]

>>> vals = (1,3,4)

>>> db.execute("SELECT col2 FROM tab WHERE col1 IN (?)", vals).fetchall()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
sqlite3.ProgrammingError: Incorrect number of bindings supplied. The current statement uses 1, and there are 3 supplied.

>>> db.execute("SELECT col2 FROM tab WHERE col1 IN (?)", (vals,)).fetchall()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
sqlite3.InterfaceError: Error binding parameter 0 - probably unsupported type.

>>> db.execute("SELECT col2 FROM tab WHERE col1 IN (?)", (','.join(str(val) for val in vals),)).fetchall()
[]

>>> 

现在我可以做到以下几点，（我认为……如果我错了请纠正我）保留了内置参数替换的安全性，但它仍然有点难看：

>>> db.execute("SELECT col2 FROM tab WHERE col1 IN (" + ",".join("?"*len(vals)) + ")", vals).fetchall()
[(u'one',), (u'three',), (u'four',)]
>>> 

这是我最好的选择，还是有更好的解决方法？

Answer 1

这是您的最佳选择无需使用额外的库。我过去肯定有advocated just that technique，实际上是more than once。

您也可以改用 SQLAlchemy，它会为您生成 SQL，但这需要您爬上它的学习曲线并重写您的大部分应用程序。

Answer 2

一个简单而干净的解决方案是：

vals = [1,3,4]
cursor.execute('SELECT col2 FROM tab WHERE col1 IN {}'.format(str(tuple(vals))