Conditional Inner join in sqlite python - python-3.x

Question

I have three tables a, b and c.
Table a is related with table b through column key.
table b is related with table c through columns word, sense and speech. In addition table c holds column id.
Now some rows in a.word have no matching value with b.word, based on that
I want to inner join tables on condition if a.word = b.word then join, otherwise compare only a.end_key = b.key.
As a result I want to have table in form of a with extra columns of start_id and end_id from c matching with key_start and key_end.
I tried following sql command with python:
CREATE TABLE relations
AS
SELECT * FROM
c
INNER JOIN
a
INNER JOIN
b
ON
a.end_key = b.key
AND
a.start_key = b.key
AND
b.word = c.word
AND
b.speech = c.speech
AND
b.sense = c.sense
OR
a.word = b.word
a:
+-----------+---------+------+-----------+
| key_start | key_end | word | relation |
+-----------+---------+------+-----------+
| k5 | k1 | tree | h |
| k7 | k2 | car | m |
| k200 | k3 | bad | ho |
+-----------+---------+------+-----------+
b:
+-----+------+--------+-------+
| key | word | speech | sense |
+-----+------+--------+-------+
| k5 | sky | a | 1 |
| k2 | car | a | 1 |
| k3 | bad | n | 2 |
+-----+------+--------+-------+
c:
+----+---------+--------+-------+
| id | word | speech | sense |
+----+---------+--------+-------+
| 0 | light | a | 1 |
| 0 | dark | b | 3 |
| 1 | neutral | a | 2 |
+----+---------+--------+-------+
Edit for clarification:
The values of tables a, b and c hold hundreds thousands lines, so there are matching values in the tables. Table a is related to table b with end_key ~ key and start_key~key relation. Table b is related to c through word sense and speech, there are values which match in each of these columns.
The desired table is in form
start_id|key_start|key_end|end_id|relation
Where start_id matches key_start and key_end matches end_id.

Answer 1

EDIT new answer
The problem with the proposed query lies in the use of AND's and OR's (and likely missing (...)). This statement
a.word = b.word then join, otherwise compare only a.end_key = b.key.
would translate to:
AND (a.word= b.word OR a.end_key = b.key).
Maybe try it like this:
ON
b.word = c.word
AND
b.speech = c.speech
AND
b.sense = c.sense
AND
(a.word = b.word OR a.end_key = b.key)
It would be a good idea to test in a sqlite manager (eg command line sqlite3, DB Browser for sqlite) before you try it in python; troubleshooting is much easier. And of course test the SELECT before you implement it in a CREATE TABLE.
You could clarify your question by showing the desired columns and result in relations table that this sample data would create (there is nothing between b and c that would match on word, speech, sense). Also the description of the relationship between a and b is confusing. In the first paragraph it says Table a is related with table b through column key. Should key be word?