内部加入三个表在mysql中耗时太长

Question

我正在查询mysql中的3个表。

SELECT t1.some_col
,t2.some_col
,t3.some_col

FROM t1, t2, t3
WHERE t1.a_col = t2.a_col AND t2.a_col = t3.a_col
AND a filter on t1
AND a filter on t2
AND a filter on t3

这花费了太多时间。 （10分钟后甚至没有给出结果）。任何优化建议都会很棒。

表t1（.3m行），t2（1.1m）和t3（258行）。没有表有索引，即使我不允许创建索引。

编辑（顺便说一下，嗯？）：

SELECT t2.parent_customerID ,
aggregate(t1.some_columns) 
FROM t1, t2, t3 
WHERE t1.customerID = t2.customerID 
AND t2.parent_customerID = t3.parent_customerID 

AND t1_where_entity_type_customer 
AND t2_parent_customer_belonging_a_region_filter 
AND t3_a_flag_check_on_parent_customer 
GROUP BY t2.parent_customer

Answer 1

尝试这种方法。

SELECT t1.some_col
,t2.some_col
,t3.some_col
FROM t1 
INNER JOIN t2 ON t1.a_col = t2.a_col
INNER JOIN t3 ON t2.a_col = t3.a_col
WHERE a filter on t1 AND a filter on t2 AND a filter on t3

Answer 2

尝试更改where条件的顺序。

SELECT t1.some_col
      ,t2.some_col
      ,t3.some_col
FROM t1, t2, t3
WHERE a filter on t1
  AND a filter on t2
  AND a filter on t3
  AND t1.a_col = t2.a_col 
  AND t2.a_col = t3.a_col;