索引的重要性
<h1>索引的重要性</h1>
<p>1>无索引查询1000万条数据</p>
<table>
<thead>
<tr>
<th>数据量</th>
<th>查询语句</th>
<th>耗时</th>
<th></th>
</tr>
</thead>
<tbody>
<tr>
<td>1310720</td>
<td>select count(*) from agency where name ='1'</td>
<td>0.418s</td>
<td></td>
</tr>
<tr>
<td>2310720</td>
<td>同上</td>
<td>0.737s</td>
<td></td>
</tr>
<tr>
<td>3310720</td>
<td>同上</td>
<td>1.058s</td>
<td></td>
</tr>
<tr>
<td>4310720</td>
<td>同上</td>
<td>1.383s</td>
<td></td>
</tr>
<tr>
<td>5310720</td>
<td>同上</td>
<td>1.715s</td>
<td></td>
</tr>
<tr>
<td>6310720</td>
<td>同上</td>
<td>2.021s</td>
<td></td>
</tr>
<tr>
<td>7310720</td>
<td>同上</td>
<td>2.396s</td>
<td></td>
</tr>
<tr>
<td>8310720</td>
<td>同上</td>
<td>2.673s</td>
<td></td>
</tr>
<tr>
<td>9310720</td>
<td>同上</td>
<td>2.991s</td>
<td></td>
</tr>
<tr>
<td>10310720</td>
<td>同上</td>
<td>3.363s</td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p>2>有索引查询1000万条数据</p>
<table>
<thead>
<tr>
<th>数据量</th>
<th>查询语句</th>
<th>耗时</th>
<th></th>
</tr>
</thead>
<tbody>
<tr>
<td>1310720</td>
<td>select count(*) from agency where name ='1'</td>
<td>0.045s</td>
<td></td>
</tr>
<tr>
<td>2310720</td>
<td>同上</td>
<td>0.078s</td>
<td></td>
</tr>
<tr>
<td>3310720</td>
<td>同上</td>
<td>0.108s</td>
<td></td>
</tr>
<tr>
<td>4310720</td>
<td>同上</td>
<td>0.145s</td>
<td></td>
</tr>
<tr>
<td>5310720</td>
<td>同上</td>
<td>0.177s</td>
<td></td>
</tr>
<tr>
<td>6310720</td>
<td>同上</td>
<td>0.206s</td>
<td></td>
</tr>
<tr>
<td>7310720</td>
<td>同上</td>
<td>0.238s</td>
<td></td>
</tr>
<tr>
<td>8310720</td>
<td>同上</td>
<td>0.272s</td>
<td></td>
</tr>
<tr>
<td>9310720</td>
<td>同上</td>
<td>0.304s</td>
<td></td>
</tr>
<tr>
<td>10310720</td>
<td>同上</td>
<td>0.342s</td>
<td></td>
</tr>
<tr>
<td>20310720</td>
<td>同上</td>
<td>0.699s</td>
<td></td>
</tr>
<tr>
<td>35165812</td>
<td>同上</td>
<td>0.976s</td>
<td></td>
</tr>
<tr>
<td>40310720</td>
<td>同上</td>
<td>11.040</td>
<td></td>
</tr>
<tr>
<td>55165812</td>
<td>同上</td>
<td>2.382</td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<table>
<thead>
<tr>
<th>数据量</th>
<th>查询语句</th>
<th>耗时</th>
</tr>
</thead>
<tbody>
<tr>
<td>55165812</td>
<td>select count(id) from agency where name ='1' limit 1000</td>
<td>1.818s</td>
</tr>
<tr>
<td>45165812</td>
<td>同上</td>
<td>1.995s</td>
</tr>
<tr>
<td>35165812</td>
<td>同上</td>
<td>1.280s</td>
</tr>
<tr>
<td>25165812</td>
<td>同上</td>
<td>0.96s</td>
</tr>
<tr>
<td>15165812</td>
<td>同上</td>
<td>0.574s</td>
</tr>
<tr>
<td>5075812</td>
<td>同上</td>
<td>0.169s</td>
</tr>
<tr>
<td>1075812</td>
<td>同上</td>
<td>0.046s</td>
</tr>
</tbody>
</table>