Question

我有两张桌子＆＃34;用户＆＃34;并且＆＃34;用户设置＆＃34;

我希望选择用户设置所在的用户什么查询会更快？

SELECT u.*, us.someSettings FROM User u,UserSettings us 
WHERE u.id = us.user_id 
AND us.somesettings = somevalue 
AND u.someProperty = someOtherValue
AND u.someProperty1 = someOtherValue1
AND u.someProperty2 = someOtherValue2
AND u.someProperty3 = someOtherValue3
AND u.someProperty4 = someOtherValue4
AND us.someUSProperty  = someUSvalue

OR

SELECT u.*, us.someSettings FROM User u
LEFT JOIN UserSettings us ON us.user_id = u.id
WHERE us.somesettings = somevalue 
AND u.someProperty = someOtherValue
AND u.someProperty1 = someOtherValue1
AND u.someProperty2 = someOtherValue2
AND u.someProperty3 = someOtherValue3
AND u.someProperty4 = someOtherValue4
AND us.someUSProperty  = someUSvalue

你能帮帮我吗？谢谢

Answer 1

正确的查询是内部联接：

SELECT u.*, us.someSettings
FROM User u INNER JOIN
     UserSettings us
     ON us.user_id = u.id
WHERE us.somesettings = somevalue 
AND u.someProperty = someOtherValue
AND u.someProperty1 = someOtherValue1
AND u.someProperty2 = someOtherValue2
AND u.someProperty3 = someOtherValue3
AND u.someProperty4 = someOtherValue4
AND us.someUSProperty  = someUSvalue;

您在UserSetting上有过滤条件，因此无论如何外部联接都会转到内部联接。您应该避免使用隐式join语法，并将连接条件显式放在on子句中。这是为了可读性和可维护性。两个版本都应具有相同的性能。

使用mysql将是连接表的最快方法

1 个答案: