EXPLAIN SELECT * 
FROM table1
INNER JOIN table2 ON table1.pid = table2.pid
LEFT JOIN table3 ON table1.pid = table3.pid
WHERE MATCH (
table3.title, table3.content
)
AGAINST (
'+words'
IN BOOLEAN
MODE
)
ORDER BY table3.pid

id select_type    table    type    possible_keys    key    key_len     ref            rows    Extra
1  SIMPLE    table1    ALL    pid            NULL    NULL     NULL             201497    Using temporary; Using filesort
1  SIMPLE    table2    ref    pid            pid    32     mydb.table1.pid    1     
1  SIMPLE    table3    ref    pid            pid    32     mydb.table2.pid             222309    Using where

SELECT * FROM 
  (SELECT table1.id as id1 
    FROM table1 
    INNER JOIN table2 
    ON table1.id = table2.id)  t1
JOIN 
  (SELECT ROUND(RAND() * (SELECT MAX(table1.id) FROM table1)) AS id2) t2 
WHERE t1.id1 >= t2.id2
LIMIT 1

------解决方案--------------------
SELECT *  
FROM table1
INNER JOIN table2 ON table1.pid = table2.pid
这样的速度呢？实在不行，就拆开来写吧。

------解决方案--------------------
呃.left join 和不用的效果一样只存在概率事件。就看你具体表及字段的设计方式了。
left join :以左表为基础，从右表找出on关键字相同的值进行匹配
from a,b呢，不存在匹配，取两个表的记录乘积。

------解决方案--------------------
SELECT *  
FROM table1
USE INDEX(PRIMARY) JOIN table2 ON table1.pid = table2.pid
这样试试看