JOIN 与 INNER JOIN 及隐式连接的区别

如果你说的是写 INNER 和不写 INNER 的话，没有区别：

SELECT * FROM A AS a JOIN B AS b ON a.id = b.pid
-- 等同于下面的一句
SELECT * FROM A AS a INNER JOIN B AS b ON a.id = b.pidCode language: PHP (php)

如果说的是隐式连接（逗号分隔 + WHERE 条件）：

SELECT * FROM A AS a, B AS b WHERE a.id = b.pidCode language: PHP (php)

语句简单时区别也不很大，因为执行时数据库通常会把它当成 INNER JOIN 执行。