Real error masked somewhere in the library with 2014
dannystaple opened this issue · comments
I've found a reproducible error case where an error that should be simple SQL syntax is masked and made very hard to spot by giving a rather mysterious:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
_mysql_exceptions.ProgrammingError: (2014, "Commands out of sync; you can't run this command now")"
What I expected:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
_mysql_exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ';)' at line 1")
Minimal case to reproduce this:
(assume you have a blank db, and have created only a connection to the db, called conn)
>>> conn.query("Create table foo(bar int(11))")
>>> conn.query("insert into foo values (1););")
>>> conn.query("insert into foo values (2););")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
_mysql_exceptions.ProgrammingError: (2014, "Commands out of sync; you can't run this command now")
I realise this is bad syntax, but it was generated and from the error I couldn’t tell that that was the problem.
The real problem here is, you're using the low-level interface and not the DB-API interface. When using the low-level interface, you're responsible for fetching the result set after each query.
Read PEP-249 and try again.
I'd reduced it to the simplest possible reproducing code. I'll set up a local environment on my current machine, and see if I can reproduce it using a cursor and execute - if I recall correctly, I did see it with using that method too.
This was simpler than the simplest possible example.
Your queries don't need statement terminators either, e.g. the trailing semicolon.
Ok - I have confirmed - I can reproduce the same behaviour using a cursor.
cu = conn.cursor()
cu.execute("create table foo(bar int(11))")
cu.execute("insert into foo values (1););")
cu.execute("insert into foo values (2););")
Will also result in _mysql_exceptions.ProgrammingError: (2014, "Commands out of sync; you can't run this command now").
No, it's working correctly. Your semicolons are creating multiple statements, so multiple result sets are returned. Your first insert works. Never mind that insert returns no rows: Every MySQL statement returns (at least) one result set; in this case, an empty (zero rows) result set. Internally, MySQLdb retrieves a result set after each .execute () call. This query returns two result sets, but the second is not retrieved; .nextset () does this. When the second insert statement is encountered, there is still a pending result set; thus the error which arises from the MySQL C API.
Try disabling multi statement support and you'll get the expected result.
My sample could be simpler - the last query doesn't need to do anything other than "select 1".
It seems that this could be a trap for someone parsing and altering large mysql dump outputs.