Python中的sqlite3 [英] sqlite3 in Python
问题描述
如何检查数据库文件是否已经存在?而且,如果它存在,我如何检查它是否已经有一个特定的表?
要查看数据库是否存在,可以sqlite3.connect
到您认为包含数据库的文件,并尝试对其运行查询.如果它不是一个数据库,你会得到这个错误:
sqlite3.connect
将创建数据库,如果它不存在;正如@johnp 在评论中指出的那样,os.path.exists
会告诉你文件是否存在.
要检查现有表,您可以查询 sqlite_master.例如:
<预><代码>>>>定义 foo(名称):...对于 c.execute("SELECT name FROM sqlite_master WHERE type='table'") 中的行:...如果行==(名称,):...返回真...返回假...>>>foo("tz_data")真>>>foo("asdf")假的How do I check if the database file already exists or not? And, if the it exists, how do I check if it already has a specific table or not?
To see if a database exists, you can sqlite3.connect
to the file that you think contains the database, and try running a query on it. If it is not a database, you will get this error:
>>> c.execute("SELECT * FROM tbl")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
sqlite3.DatabaseError: file is encrypted or is not a database
sqlite3.connect
will create the database if it doesn't exist; as @johnp points out in the comments, os.path.exists
will tell you whether the file exists.
To check for existing tables, you query against sqlite_master. For example:
>>> def foo(name):
... for row in c.execute("SELECT name FROM sqlite_master WHERE type='table'"):
... if row == (name,):
... return True
... return False
...
>>> foo("tz_data")
True
>>> foo("asdf")
False
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