问题
I just debugging a legacy code and I found a strange part in it. Does anybody has an idea, what does the following mean in the MYSQL string?
full_name LIKE '%%{fullname}%%'
回答1:
As in the answer Mihir Dave's comment links to, there's no difference to SQL if you pass %% instead of %. Since a single % matches zero or more characters, then each of the metacharacters in %% would also match zero or more, and ultimately the same string would match one way or another.
But I'd guess your legacy code is pre-Python 2.6 that uses % as a metacharacter in string formatting, and you have to double it like %% to get a single literal % character.
See also:
- How can I selectively escape percent (%) in Python strings?
- https://docs.python.org/2.6/library/stdtypes.html#string-formatting-operations
回答2:
I doubt that it is a legacy issue. I have used double percent in python 3.7 as well, though admittedly on an older mysql version, with double percent having the only function of escaping the second %. I came to this by Python3.8, MySQL5.7: passing active wildcards to LIKE query
来源：https://stackoverflow.com/questions/50863249/mysql-like-with-double-percent