相关疑难解决方法(0)

为简单起见,假设所有相关字段都是NOT NULL.

你可以做:

SELECT
    table1.this, table2.that, table2.somethingelse
FROM
    table1, table2
WHERE
    table1.foreignkey = table2.primarykey
    AND (some other conditions)

要不然:

SELECT
    table1.this, table2.that, table2.somethingelse
FROM
    table1 INNER JOIN table2
    ON table1.foreignkey = table2.primarykey
WHERE
    (some other conditions)

这两个是以同样的方式工作MySQL吗？

我有三个名为的表

**Student Table**
-------------
id    name
-------------
1     ali
2     ahmed
3     john
4     king

**Course Table**
-------------
id    name
-------------
1     physic
2     maths
3     computer
4     chemistry

**Bridge**
-------------
sid    cid
-------------
1     1
1     2
1     3
1     4
2     1
2     2
3     3
3     4
4     1
4     2

现在用他研究过的课程名称来显示学生姓名,

**Result**
---------------------------
Student        Course
---------------------------
ahmed         physic
ahmed         maths
ahmed         computer
ahmed         chemistry
ali           physic
ali           maths
john          computer
john          chemistry
king          physic
king          maths …

我想知道SQL在这些连接语句上执行的方式是否有任何不同:

SELECT * FROM a,b WHERE a.ID = b.ID

SELECT * FROM a JOIN b ON a.ID = b.ID

SELECT * FROM a JOIN b USING(ID)

有性能差异吗？还是算法差异？

或者只是语法糖？