如何优化左连接的sql？

Question

我有两个tablephone和phone_area

phone 列：

id: pk

phone: unique index

phone数据：

|id| phone       |
+--+-------------+
|1 | 1882601xxxx |
+--+-------------+
|2 | 1882602xxxx |
+--+-------------+
|2 | 1882602xxxx |
+--+-------------+
|2 | 1882603xxxx  | 
+--+-------------+

phone_area 列：

1.id: pk

2.phone: unique index

3.area: varchar(20)

phone_area数据：

|id| phone  |  area    |  
+--+--------+----------+
|1 | 1882601|  area_one|
+--+--------+----------+
|2 | 1882602|  area_two|
+--+--------+----------+ 
|2 | 1882603|area_three|
+--+--------+----------+

我的 sql 正在关注：

SELECT t1.phone,t2.area FROM phone t1
LEFT JOIN phone_area t2 ON substr(t1.phone, 1, 7)= t2.phone

速度很慢

解释sql时，显示type为"ALL"，Using where;使用连接缓冲区（块嵌套循环）

如何提高我的sql？

Answer 1

按照以下步骤操作：

ALTER TABLE phone ADD phone_cut int; --add a new column

UPDATE phone SET phone_cut = substr(phone, 1, 7); --store the cropped value of phone

ALTER TABLE phone ADD INDEX ind_name (phone_cut); -- add an index on that column

然后：

SELECT t1.phone,t2.area FROM phone t1
LEFT JOIN phone_area t2
 ON t1.phone_cut= t2.phone

如何优化左连接的sql？

How to optimize sql of left join?

mysql

left-join