sqlite - python - full outer join with attaching a database - python-2.7

Question

I have 2 tables in 2 databases:
table call in history.db:
ROWID | ADDRESS | DATE
1 | +98765 | 1396771532
2 | +98765 | 1396771533
3 | +98765 | 1396771534
4 | +98765 | 1396771535
5 | +98765 | 1396771536
6 | +98765 | 1396771537
7 | +98765 | 1396771538
8 | +98765 | 1396771539
9 | +98765 | 1396771510
table info in voices.db:
ID | CALLID | PATH | CODE
1 | 2 | voice1.m4a | 12234
2 | 5 | voice2.m4a | 12234
3 | 1 | voice4.m4a | 89765
First, I did an attach:
conn = sqlite3.connect("history.db")
conn.row_factory = sqlite3.Row
cursor = conn.cursor()
cursor.execute("attach ? as voice", ("voices.db",))
conn.commit()
Then, I joined 2 tables:
cursor.execute("SELECT * FROM call c JOIN (SELECT PATH, CALLID, CODE FROM voice.info WHERE CODE = ?) f ON c.ROWID = f.CALLID ORDER BY c.DATE", ("12234",))
So, I got the following result:
ROWID | ADDRESS | DATE | PATH | CALLID | CODE
2 | +98765 | 1396771533 | voice1.m4a | 2 | 12234
5 | +98765 | 1396771536 | voice2.m4a | 5 | 12234
But, I need a full outer join to get something like:
ROWID | ADDRESS | DATE | PATH | CALLID | CODE
1 | +98765 | 1396771532 | NULL | NULL | NULL
2 | +98765 | 1396771533 | voice1.m4a | 2 | 12234
3 | +98765 | 1396771534 | NULL | NULL | NULL
4 | +98765 | 1396771535 | NULL | NULL | NULL
5 | +98765 | 1396771536 | voice2.m4a | 5 | 12234
6 | +98765 | 1396771537 | NULL | NULL | NULL
7 | +98765 | 1396771538 | NULL | NULL | NULL
8 | +98765 | 1396771539 | NULL | NULL | NULL
9 | +98765 | 1396771510 | NULL | NULL | NULL
I tried this, but I got an error of ... UNION do not have same number result columns ....
How could I have a full outer Join?
I am using Python 2.7, so
Right and FULL OUTER JOINs are not currently supported

Answer 1

Your original query is badly written. Write it like this:
SELECT c.*, i.* FROM CALL c
JOIN voice.info i ON i.CODE = ? AND c.ROWID = i.CALLID
ORDER BY c.DATE;
Now transforming it into the full outer join as in the answer you linked is trivial:
SELECT c.*, i.* FROM CALL c
LEFT JOIN voice.info i ON c.ROWID = i.CALLID AND i.CODE = ?
UNION
SELECT c.*, i.* FROM voice.info i
LEFT JOIN CALL c ON c.ROWID = i.CALLID
WHERE i.CODE = ?;
In the answer you linked they use UNION ALL, which keeps duplicates in the result set. I don't think you want that, so therefore I prefer to use UNION, which removes duplicates (rows where all the columns are equal).
Also: it's actually even better to write out all columns instead of using *, but I didn't do that here for brevity.