Mysql5.7 order by 影響 產生 ICP

 

 

Mysql5.7 再用order by時候 ，有一種情況 會對已用索引的條件進行ICP處理，正常不應該出現，Mysql8.0無此現象產生

 

示例如下：

--orderid有普通索引，ct字段無索引，主鍵是id
create table table1 (
id int not null ,
orderid varchar(10) not null,
ct int not null,
primary key(id),
key idx_orderid(orderid)
);


insert into table1 values(1,'1111111111',11);
insert into table1 values(2,'1111111112',12);
insert into table1 values(3,'1111111113',13);
insert into table1 values(4,'1111111114',14);
insert into table1 values(5,'1111111115',15);
insert into table1 values(6,'1111111116',16);


--5.7測試

--沒有order by就不出現Using index condition; 
mysql> explain select ct from table1  where orderid='1111111113' ;
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+-------+
| id | select_type | table  | partitions | type | possible_keys | key         | key_len | ref   | rows | filtered | Extra |
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | table1 | NULL       | ref  | idx_orderid   | idx_orderid | 32      | const |    1 |   100.00 | NULL  |
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)




--order by ct時候 會出現：Using index condition; 
mysql> explain select ct from table1  where orderid='1111111113' order by ct;
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+---------------------------------------+
| id | select_type | table  | partitions | type | possible_keys | key         | key_len | ref   | rows | filtered | Extra                                 |
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+---------------------------------------+
|  1 | SIMPLE      | table1 | NULL       | ref  | idx_orderid   | idx_orderid | 32      | const |    1 |   100.00 | Using index condition; Using filesort |
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+---------------------------------------+
1 row in set, 1 warning (0.02 sec)




--8.0測試

--order by ct時候 ，不會出現 Using index condition; 
mysql> explain select ct from table1  where orderid='1111111113' order by ct;
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+----------------+
| id | select_type | table  | partitions | type | possible_keys | key         | key_len | ref   | rows | filtered | Extra          |
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+----------------+
|  1 | SIMPLE      | table1 | NULL       | ref  | idx_orderid   | idx_orderid | 42      | const |    1 |   100.00 | Using filesort |
+----+-------------+--------+------------+------+---------------+-------------+---------+-------+------+----------+----------------+
1 row in set, 1 warning (0.01 sec)

 

 

下面是5.7和8.0 的 trace 對比和說明：