我有以下mySQL查询,完全正常。除了我需要添加“FORCE INDEX”,我不确定我必须在哪里做到这一点。我尝试了几乎每个位置,并始终收到mySQL错误。我做错了什么?
以下是原始查询:
$sql_select_recent_items = $db->query("SELECT * FROM (SELECT owner_id, product_id, start_time, price, currency, name, closed, active, approved, deleted, creation_in_progress FROM db_products ORDER BY start_time DESC) as resultstable
WHERE resultstable.closed=0 AND resultstable.active=1 AND resultstable.approved=1 AND resultstable.deleted=0 AND resultstable.creation_in_progress=0
GROUP BY resultstable.owner_id
ORDER BY start_time DESC");
查询以这种方式构造,以便我可以在“GROUP BY”之前执行“ORDER BY”,以防您想知道。
我需要补充的是:
FORCE INDEX (products_start_time)
我几乎没有成功地试过它,这让我相信有一些更复杂的东西我不知道?
答案 0 :(得分:55)
索引提示的语法在此处记录:
http://dev.mysql.com/doc/refman/5.6/en/index-hints.html
索引索引紧跟在表格引用之后:
SELECT * FROM (
SELECT owner_id, product_id, start_time, price, currency, name, closed,
active, approved, deleted, creation_in_progress FROM db_products
FORCE INDEX (products_start_time)
ORDER BY start_time DESC) as resultstable
WHERE resultstable.closed=0
AND resultstable.active=1
AND resultstable.approved=1
AND resultstable.deleted=0
AND resultstable.creation_in_progress=0
GROUP BY resultstable.owner_id
ORDER BY start_time DESC
警告:强>
如果您在ORDER BY
之前使用GROUP BY
来获取每个owner_id的最新条目,那么您将使用MySQL的非标准和未记录的行为来执行此操作。
不保证它将继续在MySQL的未来版本中运行,并且查询可能是任何其他RDBMS中的错误。
在greatest-n-per-group标记中搜索有关此类查询的更佳解决方案的多种解释。
答案 1 :(得分:3)
FORCE_INDEX
将在 MySQL 8 之后被弃用:
Thus, you should expect USE INDEX, FORCE INDEX, and IGNORE INDEX to be deprecated in
a future release of MySQL, and at some time thereafter to be removed altogether.
https://dev.mysql.com/doc/refman/8.0/en/index-hints.html
对于 v8,您应该使用 JOIN_INDEX
、GROUP_INDEX
、ORDER_INDEX
和 INDEX
。