mysql数据库索引的建立以及性能测试

##---------mysql学习（四）索引的建立--------### #今天突然开窍了，所以补充点索引方面的知识。 #创建索引，这里仍然以数据较少的mytab表为例： #原数据为： mysql set names gbk; Query OK, 0 rows affected (0.00 sec) mysql select * from mytab; -----

##---------mysql学习（四）索引的建立--------###
#今天突然开窍了，所以补充点索引方面的知识。
#创建索引，这里仍然以数据较少的mytab表为例：
#原数据为：
mysql> set names gbk;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from mytab;
+----+--------+-----+--------+
| id | name   | age | salary |
+----+--------+-----+--------+
|  1 | ?阿琼      |  23 |   1000 |
|  2 | 秋水虾     |  24 |    500 |
|  3 | 害人精      |  22 |    100 |
+----+--------+-----+--------+
3 rows in set (0.00 sec)
#alter  table table_name add index index_name (column)==
#create index index_name on table_name(column);
#alter创建索引示例

mysql> alter table mytab add index mytab_name (name);
Query OK, 3 rows affected (0.15 sec)
Records: 3  Duplicates: 0  Warnings: 0

#create创建索引示例：
mysql> create index mytab_id on mytab (id);
Query OK, 3 rows affected (0.16 sec)
Records: 3  Duplicates: 0  Warnings: 0

#查看索引
mysql> show index from mytab;
+-------+------------+----------+--------------+-------------+-----------+------
-------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardi
nality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+----------+--------------+-------------+-----------+------
-------+----------+--------+------+------------+---------+
| mytab |          0 | PRIMARY  |            1 | id          | A         |
     3 |     NULL | NULL   |      | BTREE      |         |
| mytab |          1 | mytab_id |            1 | id          | A         |
     3 |     NULL | NULL   |      | BTREE      |         |
+-------+------------+----------+--------------+-------------+-----------+------
-------+----------+--------+------+------------+---------+
2 rows in set (0.00 sec)

#创建unique索引
mysql> alter table mytab add unique (name);
Query OK, 3 rows affected (0.20 sec)
Records: 3  Duplicates: 0  Warnings: 0

#创建联合索引：
mysql> create index mytab_id_name on mytab (id,name);
Query OK, 3 rows affected (0.20 sec)
Records: 3  Duplicates: 0  Warnings: 0
mysql> show index from mytab;
+-------+------------+---------------+--------------+-------------+-----------+-
------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name      | Seq_in_index | Column_name | Collation |
Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+---------------+--------------+-------------+-----------+-
------------+----------+--------+------+------------+---------+
| mytab |          0 | PRIMARY       |            1 | id          | A         |
          3 |     NULL | NULL   |      | BTREE      |         |
| mytab |          0 | name          |            1 | name        | A         |
          3 |     NULL | NULL   |      | BTREE      |         |
| mytab |          1 | mytab_name    |            1 | name        | A         |
          3 |     NULL | NULL   |      | BTREE      |         |
| mytab |          1 | mytab_id_name |            1 | id          | A         |
          3 |     NULL | NULL   |      | BTREE      |         |
| mytab |          1 | mytab_id_name |            2 | name        | A         |
          3 |     NULL | NULL   |      | BTREE      |         |
+-------+------------+---------------+--------------+-------------+-----------+-
------------+----------+--------+------+------------+---------+
5 rows in set (0.00 sec)

#下面我们尝试一下删除索引，删除用drop
#drop index index_name on table_name==
#alter table table_name drop index index_name;

#drop示例：
mysql> drop index mytab_id on mytab;
Query OK, 3 rows affected (0.17 sec)
Records: 3  Duplicates: 0  Warnings: 0

#alter示例：
mysql> alter table mytab drop index mytab_id_name;
Query OK, 3 rows affected (0.17 sec)
Records: 3  Duplicates: 0  Warnings: 0

#现在发现由于数据数量较小，根本无法判断索引存在的价值。
#
#这里我打算向其中添加3000行数据，这里需要用到Java代码：
#
| 3001 | yiha_2997 |  22 |   5997 |
| 3002 | yiha_2998 |  22 |   5998 |
| 3003 | yiha_2999 |  22 |   5999 |
+------+-----------+-----+--------+
3003 rows in set (0.01 sec)
#######################java代码段##############################
public static void main(String[] args) {
  Connection conn=DBConnection.getConnection();
  try {
   conn.setAutoCommit(false);
   PreparedStatement state=conn.prepareStatement
    ("insert into mytab(name,age,salary) values (?,?,?)");
   for(int i=0;i    state.setString(1,"yiha_"+i );
   state.setInt(2, 22);
   state.setInt(3, 3000+i);
   state.addBatch();
   }
   state.executeBatch();
   conn.commit();
   state.close();
  } catch (SQLException e) {
   e.printStackTrace();
  }
 }
######################数据库连接connection######################
private static String url="jdbc:mysql://" +
   "localhost:3306/mydb?useUnicode=true&characterEncoding=UTF-8";
 private static String driver="com.mysql.jdbc.Driver";
 private static String name="root";
 private static String pwd="root";
 public static Connection getConnection(){
  Connection conn;
  try {
   Class.forName(driver).newInstance();
   conn = DriverManager.getConnection(url, name, pwd);
   return conn;

###################################################################

##现在数据库中有3003条数据，我们看一下检索数据时间。
#如检索：
   id      NAME      age     salary
| 2894 | yiha_2890 |  22 |   5890 |
#id以及name为索引，但是age和salary为非索引

mysql> select * from mytab where id=2894;
+------+-----------+-----+--------+
| id   | name      | age | salary |
+------+-----------+-----+--------+
| 2894 | yiha_2890 |  22 |   5890 |
+------+-----------+-----+--------+
1 row in set (0.00 sec)

mysql> select * from mytab where salary=5890;
+------+-----------+-----+--------+
| id   | name      | age | salary |
+------+-----------+-----+--------+
| 2894 | yiha_2890 |  22 |   5890 |
+------+-----------+-----+--------+
1 row in set (0.00 sec)
#可以看出无差别，也许数据仍旧太少，现在将数据提升到30000；

mysql> select * from mytab where id=30000; #id为索引
+-------+------------+-----+--------+
| id    | name       | age | salary |
+-------+------------+-----+--------+
| 30000 | yiha_29996 |  23 |  32996 |
+-------+------------+-----+--------+
1 row in set (0.00 sec)

mysql> select * from mytab where salary=32996;#salary为非索引
+-------+------------+-----+--------+
| id    | name       | age | salary |
+-------+------------+-----+--------+
| 30000 | yiha_29996 |  23 |  32996 |
+-------+------------+-----+--------+
1 row in set (0.02 sec)
#由于name也是索引，所以这里试一下用name查找数据：

mysql> select * from mytab where name='yiha_29996';#name为索引
+-------+------------+-----+--------+
| id    | name       | age | salary |
+-------+------------+-----+--------+
| 30000 | yiha_29996 |  23 |  32996 |
+-------+------------+-----+--------+
1 row in set (0.00 sec)

##虽然在数据多次实验中能够看出索引的作用，但是并不是很明显。以上每一组所耗费时间都是
#个人寻找的出现次数最多的时间。

##个人感觉测试索引效果挺无聊的，索引的作用很多文章都只写了可以精确查找，至于索引如何
#运用貌似很少有相关的东西。数据库中的数据还可以随意扩大，个人感觉先这样吧。