At T246159 we can observe a really badly formatted query:
SELECT /* Wikibase\Lib\Store\Sql\Terms\DatabaseTermInLangIdsResolver::selectTermsViaJoin */ wbtl_id, wbtl_type_id, wbxl_language, wbx_text, wbit_item_id FROM `wbt_term_in_lang`, `wbt_text_in_lang`, `wbt_text`, `wbt_item_terms` WHERE (wbtl_text_in_lang_id=wbxl_id) AND (wbxl_text_id=wbx_id) AND wbit_item_id IN (...) AND wbxl_language IN ('hu', 'en') AND (`wbit_term_in_lang_id` = wbtl_id)
Compare this with the equivalent:
SELECT /* Wikibase\Lib\Store\Sql\Terms\DatabaseTermInLangIdsResolver::selectTermsViaJoin */ wbtl_id, wbtl_type_id, wbxl_language, wbx_text, wbit_item_id FROM wbt_term_in_lang JOIN wbt_text_in_lang ON wbtl_text_in_lang_id = wbxl_id JOIN wbt_text ON wbxl_text_id = wbx_id JOIN wbt_item_terms ON wbit_term_in_lang_id = wbtl_id WHERE wbit_item_id IN (...) AND wbxl_language IN ('hu', 'en')
(ignore the quotation and justification, plus I don't know by heart the right columns of each table). It is funny that a method called selectTermsViaJoin didn't contain any join! :-)
While this could be disregarded as a minor issue, I would like to direct your attention to this issue for 2 reasons:
- A badly formatted query like this has been the direct cause of outages at wikimedia database infrastructure. By convention (outside of Wikimedia, but specially on Wikimedia) implicit JOINS are highly discouraged. I don't know how even the wikimedia abstraction layer allows them.
JOINS should be explicit and be used with its ON clause. In the past, the removal of an ON clause but not removal from the implicit list of tables to join caused overload and an outage. As a preventive measure, this was considered a bad practice and discouraged. This is also a standard among any serious professional SQL work. This is hard to read, to the point I could not work with the query. JOIN ... ON is way more legible. You know with a single view which tables are involved and differenciate filtering from joining comparisons, preventing mistakes when changing the query.
- This issue would have been caught immediately by DBAs or other developers on review and asked to be changed immediately. This leads to the more important issue that review process may be broken because not even the most obvious formatting issue has been corrected on review. I am not looking to assign any blame here, I am asking to review the reviewing process for database layer changes so obvious mistakes like these are caught on time.
- the sql should explicitly JOIN and ON keywords instead of doing the join by some implicit SQL-Magic