mysql update 有无索引对比

<pre name="code" class="html">mysql> desc ProductInfo;
+----------------+--------------+------+-----+---------+-------+
| Field          | Type         | Null | Key | Default | Extra |
+----------------+--------------+------+-----+---------+-------+
| sn             | int(11)      | NO   | PRI | NULL    |       |
| productIntro   | text         | NO   |     | NULL    |       |
| borrowerInfo   | text         | NO   |     | NULL    |       |
| realBorrower   | varchar(128) | YES  |     | NULL    |       |
| capitalPurpose | text         | NO   |     | NULL    |       |
| repaySource    | text         | NO   |     | NULL    |       |
| riskInfo       | text         | NO   |     | NULL    |       |
| safeguard      | varchar(50)  | NO   |     |         |       |
| contractSn     | int(11)      | YES  |     | NULL    |       |
| delegator      | int(11)      | NO   |     | NULL    |       |
| custody        | varchar(125) | NO   |     |         |       |
| riskLevel      | char(1)      | NO   |     | NULL    |       |
+----------------+--------------+------+-----+---------+-------+
12 rows in set (0.00 sec)

mysql> show index from ProductIno;
ERROR 1146 (42S02): Table 'zjzc.ProductIno' doesn't exist
mysql> show index from ProductInfo;
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table       | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| ProductInfo |          0 | PRIMARY  |            1 | sn          | A         |         283 |     NULL | NULL   |      | BTREE      |         |               |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.01 sec)

mysql> select sn,contractSn from ProductInfo where  contractSn=45;
+-----+------------+
| sn  | contractSn |
+-----+------------+
|  58 |         45 |
| 301 |         45 |
+-----+------------+
2 rows in set (0.00 sec)

mysql> explain update ProductInfo set contractSn=99 where contractSn=45;
+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+
| id | select_type | table       | type  | possible_keys | key     | key_len | ref  | rows | Extra       |
+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+
|  1 | SIMPLE      | ProductInfo | index | NULL          | PRIMARY | 4       | NULL |  283 | Using where |
+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+
1 row in set (0.07 sec)

mysql> create index ProductInfo_idx1 on ProductInfo(contractSn);
Query OK, 0 rows affected (0.23 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> explain update ProductInfo set contractSn=99 where contractSn=45;
+----+-------------+-------------+-------+------------------+------------------+---------+-------+------+------------------------------+
| id | select_type | table       | type  | possible_keys    | key              | key_len | ref   | rows | Extra                        |
+----+-------------+-------------+-------+------------------+------------------+---------+-------+------+------------------------------+
|  1 | SIMPLE      | ProductInfo | range | ProductInfo_idx1 | ProductInfo_idx1 | 5       | const |    2 | Using where; Using temporary |
+----+-------------+-------------+-------+------------------+------------------+---------+-------+------+------------------------------+
1 row in set (0.00 sec)

/***************************************************************************************************8

mysql> show create  table test100\G;
*************************** 1. row ***************************
       Table: test100
Create Table: CREATE TABLE `test100` (
  `sn` int(11) NOT NULL COMMENT 'product sn',
  `productIntro` text NOT NULL COMMENT '产品介绍',
  `borrowerInfo` text NOT NULL COMMENT '借款方信息',
  `realBorrower` varchar(128) DEFAULT NULL COMMENT '实际借款人',
  `capitalPurpose` text NOT NULL COMMENT '资金用途',
  `repaySource` text NOT NULL COMMENT '还款来源',
  `riskInfo` text NOT NULL COMMENT '风控信息',
  `safeguard` varchar(50) NOT NULL DEFAULT '' COMMENT '保障信息代码列表，格式1,2,3,4',
  `contractSn` int(11) DEFAULT NULL COMMENT '合同模版',
  `delegator` int(11) NOT NULL COMMENT '产品委托人',
  `custody` varchar(125) NOT NULL DEFAULT '' COMMENT '产品管理人',
  `riskLevel` char(1) NOT NULL COMMENT '风险级别'
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

ERROR:
No query specified

mysql> show index from test100;
Empty set (0.00 sec)

mysql>  explain update test100 set contractSn=99 where contractSn=45;
+----+-------------+---------+------+---------------+------+---------+------+------+-------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+---------+------+---------------+------+---------+------+------+-------------+
|  1 | SIMPLE      | test100 | ALL  | NULL          | NULL | NULL    | NULL |  283 | Using where |
+----+-------------+---------+------+---------------+------+---------+------+------+-------------+
1 row in set (0.00 sec)

mysql> create index test100_idx1 on test100(contractSn);
Query OK, 0 rows affected (0.36 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>  explain update test100 set contractSn=99 where contractSn=45;
+----+-------------+---------+-------+---------------+--------------+---------+-------+------+------------------------------+
| id | select_type | table   | type  | possible_keys | key          | key_len | ref   | rows | Extra                        |
+----+-------------+---------+-------+---------------+--------------+---------+-------+------+------------------------------+
|  1 | SIMPLE      | test100 | range | test100_idx1  | test100_idx1 | 5       | const |    2 | Using where; Using temporary |
+----+-------------+---------+-------+---------------+--------------+---------+-------+------+------------------------------+
1 row in set (0.03 sec)