BUG: fix read_sql delegation for queries without select statement (GH7324)

[jorisvandenbossche]

Closes #7324.

The if 'select' in ...' check was introduced for mysql legacy compatibility, but introduced problem if the query did not contain a select statement (eg a stored procedure). This should solve this, and passes the test suite (locally).

[jreback]

you mean #7324, rigtht?

[jorisvandenbossche]

yep, changed

[hayd]

should add something to release? otherwise looks good!

[jorisvandenbossche]

yep, and maybe also a small test with a stored procedure

[jorisvandenbossche]

added release note and test. Only problem for now is that the test is not working (see failed travis). Strange thing is that I get a Command out of sync error when I call read_sql("CALL proc") (https://github.com/jorisvandenbossche/pandas/blob/sql-delegation/pandas/io/tests/test_sql.py#L1097) after creating the procedure with engine.execute(proc) (which resultproxy is automatically closed by sqlalchemy). And If I run the read_sql a second time, it is OK. @hayd @danielballan any idea? (I can just add a try: .. except: pass for the first call, but that seems not really correct)

[danielballan]

My guess is something with transactions. I spent a few minutes today and couldn't get it. I could be wrong, but I thought I'd share that thought in case someone has more time to look at this before I revisit it.

[jorisvandenbossche]

@danielballan Thanks for the pointer, that solved it.

I tested the following approaches:

engine.execute(proc)

with engine.begin() as connection:
    connection.execute(proc)

connection = engine.connect()
trans = connection.begin()
try:
    r1 = connection.execute(proc)
    trans.commit()
except:
    trans.rollback()
    raise

And only the last did work, although I don't fully understand why, as I would think the other should be equivalent (http://docs.sqlalchemy.org/en/rel_0_8/core/connections.html#using-transactions), as sqlalchemy autocommits by default. But in any case, it works now (and it was only for the test, so not that important).