Insert from_select Mysql returns number of rows affected, instead of lastrowid/pk

Using an insert_from with mysql will always return the number of rows inserted, instead of returning the lastrowid. Postgresql instead will return a result cursor from which you can derive the lastrowid. So if we use the insert_from style with MySQL there is no way to obtain the lastrowid using the public API.

In Mysql:

# this will correctly return the lastrowid/pk:
Users.insert(name='foo').execute()

# this will always return 1, instead of the lastrowid/pk. 
Users.insert_from(
    Select(columns=['a']),
    ['name']
).execute()

With Postgresql, the behavior is different, presumably because postgresql will automatically add a returning (which is not available in mysql).

# This will return the PK, same as mysql:
Users.insert(name='foo').execute()

# This returns ModelTupleCursorWrapper
res = Users.insert_from(
    Select(columns=['a']),
    ['name']
).execute()

# get the pk
print(list(res)[0][0])

# let's get rid of the RETURNING clause, and the behavior is the same as mysql, which is to return 1:
res = Users.insert_from(
    Select(columns=['a']),
    ['name']
).returning().execute()

[coleifer]

Off the top of your head, do you know if I would be able to detect if a user is using MariaDB?

Sure:

conn = db.connection()  # Get db-api2 conn
print(conn.server_version) # or
print(conn.get_server_info())
# 5.5.5-10.7.3-MariaDB-1:10.7.3+maria~bullseye-log

[coleifer]

The issue with the query execution I believe is fixed in 3.36 and is far more concerning than the error code. So if you check for 3.36 or newer it may be safe to use returning everywhere.

I’m going to revisit that patch and see how things are looking when I can find some free time.