MySQL 如果存在，则删除行
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Delete row if exists
提问by Kin
DELETE IF EXIST `#__menu`.*
FROM `#__menu`
LEFT JOIN `#__extensions` ON `#__extensions`.`name` = 'com_view'
WHERE `#__menu`.`component_id` = `#__xtensions`.`extension_id`
AND `#__menu`.`alias` = 'view-sites' AND `#__menu`.`path` = 'view-sites' AND `#__menu`.`title` = 'View sites';
What is wrong in my sql? I think the problem is in IF EXIST, but i could not figure out how to use it on row.
我的sql有什么问题？我认为问题出在IF EXIST，但我不知道如何在行上使用它。
回答by newfurniturey
When you're deleting rows from a table, you don't need to use IF EXISTS- you're using a WHEREclause, so if it exists - it will be deleted.
当您从表中删除行时，您不需要使用IF EXISTS- 您正在使用WHERE子句，因此如果它存在 - 它将被删除。
Try changing your query to:
尝试将您的查询更改为：
DELETE
FROM `#__menu`
LEFT JOIN `#__extensions` ON `#__extensions`.`name` = 'com_view'
WHERE `#__menu`.`component_id` = `#__xtensions`.`extension_id`
AND `#__menu`.`alias` = 'view-sites' AND `#__menu`.`path` = 'view-sites' AND `#__menu`.`title` = 'View sites';
Also, you don't need to specify ```#__menu.*`` (the columns) to be deleted - you'll just needDELETE FROM...`. Check out herefor more info regarding the syntax.
此外，您不需要指定```#__menu .*`` (the columns) to be deleted - you'll just needDELETE FROM...`。查看此处了解有关语法的更多信息。
