python ALTER TABLE Sqlite：如何在更改表之前检查列是否存在？
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ALTER TABLE Sqlite: how to check if a column exists before alter the table?
提问by Esabe
I need to execute in python a SQL query that adds a new column, in sqlite3.
我需要在 python 中执行一个 SQL 查询，在 sqlite3 中添加一个新列。
The problem is that sometimes it already exists. So previous to executing the query I need to check if the column already exists.
问题是有时它已经存在。所以在执行查询之前，我需要检查该列是否已经存在。
If it does, then I won't execute the query.
如果是这样，那么我将不会执行查询。
Is there a way in sqlite to do that? Or do I have to make it through a try-catch block in python code?
sqlite 有没有办法做到这一点？还是我必须通过 python 代码中的 try-catch 块来实现？
Thanks a lot in advance!
非常感谢！
回答by My Other Me
You can get a list of columns for a table via the following statement:
您可以通过以下语句获取表的列列表：
PRAGMA table_info('table_name');
More details on the pragma commands are availabel at the sqlite web site
有关 pragma 命令的更多详细信息，请访问sqlite 网站
回答by Nick Dandoulakis
IMO this
海事组织这个
conn = sqlite3.connect(':memory:')
c = conn.cursor()
try:
c.execute('ALTER TABLE mytable ADD COLUMN newcolumn;')
except:
pass # handle the error
c.close()
is a better choice than constructing special casequeries.
是比构建特殊情况查询更好的选择。
You can wrap the above code in a AddColumn(cursor, table, column) function so you can reuse it,
plus it'll make the code more readable.
您可以将上述代码包装在 AddColumn(cursor, table, column) 函数中，以便您可以重用它，
而且它会使代码更具可读性。
