有了以上信息我们就可以写出4条语句处理全部数据。为了调用接口尽量简单，建立下面的存储过程。
delimiter //
create procedure sp_unique(i smallint)
begin
set @a:='1000-01-01 00:00:00';
set @b:=' ';
if (i<4) then
insert into t_target
select * from t_source force index (idx_sort)
where created_time >= date_add('2017-01-01',interval (i-1)*125000 second)
and created_time < date_add('2017-01-01',interval i*125000 second)
and (@a!=created_time or @b!=item_name)
and (@a:=created_time) is not null
and (@b:=item_name) is not null
order by created_time,item_name;
else
insert into t_target
select * from t_source force index (idx_sort)
where created_time >= date_add('2017-01-01',interval (i-1)*125000 second)
and created_time <= date_add('2017-01-01',interval i*125000 second)
and (@a!=created_time or @b!=item_name)
and (@a:=created_time) is not null
and (@b:=item_name) is not null
order by created_time,item_name;
end if;
end
//
查询语句的执行计划如下：
mysql> explain select * from t_source force index (idx_sort)
-> where created_time >= date_add('2017-01-01',interval (http://www.amjmh.com)*125000 second)
-> and created_time < date_add('2017-01-01',interval 1*125000 second)
-> and (@a!=created_time or @b!=item_name)
-> and (@a:=created_time) is not null
-> and (@b:=item_name) is not null
-> order by created_time,item_name;
+----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-----------------------+
| 1 | SIMPLE | t_source | NULL | range | idx_sort | idx_sort | 6 | NULL | 498640 | 100.00 | Using index condition |
+----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-----------------------+
1 row in set, 3 warnings (0.00 sec)
MySQL优化器进行索引范围扫描，并且使用索引条件下推（ICP）优化查询。
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