I am using an Laravel's ORM. It is generating a huge query and inside that query I noticed that there is a WHERE statement that repeats itself, and the order of that WHERE statement seems to be very important. I believe it has something to do with how MySQL is grouping the WHERE statements but I don't understand how MySQL works well enough. I'm trying to understand why this works the way it does. How is mysql interpreting/grouping this?
Table
items
-----------------------------------------------
id | status
-----------------------------------------------
19 | 1
20 | 0
21 | 1
Results needed:
-----------------------------------------------
id | status
-----------------------------------------------
19 | 1
21 | 1
The query is much longer than this. But here is the code the ORM is generating that produces the above results needed:
SELECT * FROM campaigns WHERE status = 1 OR id IN ('20') AND status = 1 ORDER BY id DESC;
If I remove the last status = 1 the query does not return the needed results. Is MySQL grouping the WHERE statements like this:
SELECT * FROM campaigns WHERE status = 1 OR (id IN ('20') AND status = 1);
The query the ORM produces is a few pages long, so when reading this it is pretty confusing without the parentheses. It seems like MySQL is grouping it like this. I guess I don't understand well enough how MySQL works. Any recommendations on books to better understand MySQL?
Building up the Query/Trying to understand what MySQL is doing
1)
SELECT * FROM items WHERE status = 1
Results
-----------------------------------------------
id | status
-----------------------------------------------
19 | 1
21 | 1
2)
SELECT * FROM items WHERE status = 1 OR id IN ('20')
Results
-----------------------------------------------
id | status
-----------------------------------------------
19 | 1
20 | 0
21 | 1
3)
SELECT * FROM items WHERE status = 1 OR id IN ('20') AND status = 1
Results
-----------------------------------------------
id | status
-----------------------------------------------
19 | 1
21 | 1
