mysql慢查询

Question

ALTER TABLE customers ADD split INT(1);

10密耳。记录......我执行了这个命令1小时仍在加载..有什么方法可以让它更快完成？

Answer 1

以下内容非常快，耗时超过6分钟，行数为1000万行，但示例表的字段和索引比生产表少，所以如果您决定使用它，预计会花费更长的时间！

注意：该示例是在Windows操作系统上完成的，因此您必须将路径名和\ r \ n更改为\ n以符合Linux标准！

这是我现有的表格（innodb引擎ofc）：

drop table if exists customers;
create table customers
(
customer_id int unsigned not null auto_increment primary key,
name varchar(255) not null,
country_id tinyint unsigned not null default 0,
key (country_id)
)
engine=innodb;

mysql> select count(*) from customers;
+----------+
| count(*) |
+----------+
| 10000000 |
+----------+
1 row in set (1.78 sec)

创建新版本的表格，其中包含您需要的新字段：

drop table if exists customers_new;
create table customers_new
(
customer_id int unsigned not null auto_increment primary key,
name varchar(255) not null,
country_id tinyint unsigned not null default 0,
split tinyint not null default 0,
key (country_id)
)
engine=innodb;

将旧客户表中PK数据的数据导出为csv格式：

select * into outfile 'c:\\customers.dat' 
fields terminated by '|' optionally enclosed by '"'
lines terminated by '\r\n'
from customers order by customer_id;

Query OK, 10000000 rows affected (17.39 sec)

将customer.dat文件加载到新的客户表中：

truncate table customers_new;

set autocommit = 0;

load data infile 'c:\\customers.dat' 
into table customers_new
fields terminated by '|' optionally enclosed by '"'
lines terminated by '\r\n'
(
customer_id,
name,
country_id,
@dummy -- represents the new split field
)
set
name = nullif(name,'');

commit;

Query OK, 10000000 rows affected (6 min 0.14 sec)

检查一切是否正常

select * from customers_new order by customer_id desc limit 1;
+-------------+-------------------+------------+-------+
| customer_id | name              | country_id | split |
+-------------+-------------------+------------+-------+
|    10000000 | customer 10000000 |        218 |     0 |
+-------------+-------------------+------------+-------+
1 row in set (0.00 sec)

insert into customers_new (name, country_id, split) values ('f00',1,1);
Query OK, 1 row affected (0.07 sec)

select * from customers_new order by customer_id desc limit 1;
+-------------+------+------------+-------+
| customer_id | name | country_id | split |
+-------------+------+------------+-------+
|    10000001 | f00  |          1 |     1 |
+-------------+------+------------+-------+
1 row in set (0.00 sec)

删除旧表并重命名新表：

drop table customers;
Query OK, 0 rows affected (0.18 sec)

rename table customers_new to customers;
Query OK, 0 rows affected (0.05 sec)

select * from customers order by customer_id desc limit 1;
+-------------+------+------------+-------+
| customer_id | name | country_id | split |
+-------------+------+------------+-------+
|    10000001 | f00  |          1 |     1 |
+-------------+------+------------+-------+
1 row in set (0.00 sec)

这就是所有人！

Answer 2

可能不是代码..
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