View Issue Details
|ID||Project||Category||View Status||Date Submitted||Last Update|
|0003797||Composr||core_database_drivers||public||2019-04-03 19:57||2019-06-27 19:00|
|Reporter||Chris Graham||Assigned To|
|Target Version||Fixed in Version|
|Summary||0003797: Cleanup queries so can_arbitrary_groupby/remove_duplicate_rows|
|Description||In various places we use can_arbitrary_groupby and/or remove_duplicate_rows to strip out duplicated rows coming out of SQL queries.|
This is because doing JOINs on tables will multiply up rows on the main table being queried, if the joined table has multiple matching records.
For example, if you are using a JOIN to check group access to a category, and a user is in multiple groups with access, you'll get as many rows back as there are groups with access.
We do it using JOINs because MySQL did not support subqueries until 4.1 in 2003. Webhosts are notorious for running old versions of MySQL, but at this point it would be shocking for a host to be running a version this old.
So we should alter the DB drives to remove the concept of can_arbitrary_groupby (which is a non-compliant MySQL hack), and assume subquery support is always there (I think this is already done in v11). Then instead of JOINs to check things like category membership or group access, we use IN or EXISTS clauses in the queries.
main_multi_content needs changes too. This currently doesn't use can_arbitrary_groupby/remove_duplicate_rows because of the complexity in this code. Instead it has it's own deduplication technique, and always reads records from offset 0, manually skipping records up until $start.
|Time estimation (hours)||4|