索引被用来快速找出在一个列上用一特定值的行。没有索引,MySQL不得不首先以第一条记录开始并然后读完整个表直到它找出相关的行。表越大,花费时间越多。
如果表对于查询的列有一个索引,MySQL能快速到达一个位置去搜寻到数据文件的中间,没有必要考虑所有数据。如果一个表有1000 行,这比顺序读取至少快100倍。注意你需要存取几乎所有1000行,它较快的顺序读取,因为此时我们避免磁盘寻道。

例如对下面这样的一个student表:

mysql>SELECT * FROM student;

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" alt="" />

这样,我们试图对它进行一个特定查询时,就不得不做一个全表的扫描,速度很慢。
例如,我们查找出所有english成绩不及格的学生:

mysql>SELECT name,english FROM student WHERE english<60;

aaarticlea/png;base64,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" alt="" />

其中,WHERE从句不得不匹配每个记录,以检查是否符合条件。对于这个较小的表也许感觉不到太多的影响。但是对于一个较大的表,例如一个非常大的学校,我们可能需要存储成千上万的记录,这样一个检索的所花的时间是十分可观的。
如果,我们为english列创建一个索引:

mysql>ALTER TABLE student ADD INDEX (english) ;

再执行下述查询:

mysql>SELECT name,english FROM user WHERE english<60;

结果为:

aaarticlea/png;base64,iVBORw0KGgoAAAANSUhEUgAAAJcAAADqCAIAAAAgQUAxAAAJp0lEQVR4nO2dQY6jOhRFez+Ralg7QRllI1EGbAQpKwnKSrwU9wCCn40NtmMo++oe1aCKJvwHJzbwc3n5p0n7/PvrAkgBaBEBWkSAFhGgRQRoEYF9i+/H5ffxOqGUJFiVhBZLQotpsCpJ2OJ4//25OD/9eF5lrCqe1LH46lflnvhzf7dU1XlwRi0JLabBqiS8X0SAFhGgRQRoEQFaRIAWEaBFBGgRAVpEgBYRoEUEaBEBWkSAFhGgRQRoEQFaRGDD4qsXiZLqObTaV//TPZX8JbTabmjqkDppMXLjG/Lkam1YfPU/3XMcbnP8S+ybWhaKHJ8abj/dc/gE/R4vE/oz+RT1vH5eeB2U+1+MJHR0vBsP74WJ001lT9v0jEU1dL/uy1/9z6UfvJvdrfMrMiya7N77sRwa6234fnzWmdROwiZ/0++TXaWno3z7HF41dLkivdWGNr61F/P685syYHG8mwDjKGV7N7tb57fkWDSThtwZybJcDTezvnzt53d3C+p5zcvj+qoNbjywF+NdHnc1dFEWrRp2D04DFmW6d7EoJxx78hnlvGR+bjmj0VNteOP+vVBDZ+UQx40Z1UzU4j3XvMXZ3yzAGot7FvPPhTvVhjf+vcWZ90OeAlu3aM9F8RaDc3IyMTNq2l5szagWy9kXwOKy8nxd0D1VhMVpalqO3XgPXNrtEry68W08dLjl1ZC8VNk8L5p9bN2imVumPf+stm9RWzcDmQpD1YY2vnG47TsNc+3qjkWxv97Lt6otVssB1TqniTLQ4hYlqrXmc+tesxy0uEWZauXNyQEK9fkWSTPQIgK0iAAtIkCLCNAiArSIAC0iQIsI0CICtIgALSJAiwjQIgK0iAB7Mpak3p6MPF7x0GIarErCvuEIVbFv+HFVnQdn1JLQYhqsSsL7RQRoEQFaRIAWEaBFBGgRAVpEgBYRoEUEaBEBWkSAFhGgRQRoEQFaRIAWEShsUSlVdoMkhpx+N7J5ltNy+JgeMdsc2ZfH6oCmPa1DzywmTLJFO5SgntflTzyLUw85q3uc1fn4rDZvu2T1DVdiwdyzTjTNE1LnJVENu7O7hx914NTQ3R53MxY9LX3XvQfbsCgHn+efPm9VazWnMbevs/Y33cOPOXBquF0H5c6o9grNWtTWucE61sKEGm6rTtQ7Dbvzu4cfceDU87ru7+qs4H03N2NRruBOoabjtF9wuNXzKq0bfYotf+DU0Im3o785cWBCas+i1jrwnQoZFst/k0Yu01y6/O5YVMNt6x3WhEVP/12rd3ShGTWJwgfOOzHMNe83xG7CotOJ27rgjr26CTXszu0eftb94saVzjnFhPn6rt81ununEeqsnd09/CSLW2P0nGLCAPQqrqpOWsykqjppMZOq6qzOImkGWkSAFhGgRQRoEQFaRIAWEaBFBGgRAVpEgBYRoEUEaBGBtM803D5n492JOX0SNOuvY97+svRszgyGrzO3JxazSZpFJ+b0flz6x30z5H+QvK0iC+EEw+U7OJSCb8SiHYuaQptytZghKHSqJSQu0g/TCBju5l0/3sMj4KxguD0uA6G9VizKvO+c+LOXzC+J1GlyK+/HJzM+qZ2ETf6m38/MYu8Ew1sfi1q/HyZ0Ov2yZHDV0H2GS/p5cUlSqeFm7ErTdvJqs8jv2AiGf06N/vRsOxb1OJ8I3w9nUIolCRZXz5JZx06ufJLFvWC41joUoG3I4jxtOqfD6bGp9dHfmVHNJa41Fv/O4nYwXKzne5KkIYuTrVHs7TQKB7kkwqLzFEAdFoOhU89jb21b1O/H5XbtnNtEe0mcxWX788Xq+mz0BzOqwarEHnzugyjHF7NJVpJxvLuxaOuSREeeF0XGfJqiL/1YrUUd8ZxsWxYroqoiaTGTqoqkxUyqKrJGi6QZaBEBWkSAFhGgRQRoEQFaRIAWEaBFBGgRAVpEgBYR+DOL7DBekIJ9w3dZPvKVSUDvZ7/xG/yLjuGVBcN10b7h8dRv0QmGu+3R6+lvO1Gqb3hMpnt6rfO0w6v/ufSDt5P4LmcFw53oVE29pifK9Q3fz3QHZ1RfJ/EYTgqGr/L8dQXgdMm+4fuZ7ojzYlq727OC4Z6x2LxFucIl8ByFN7vWgMVAMPzV/9hNe4Esaq3F3gJY3AqGmxmoH+sKhuuSfcPbtxjXjXjdFf2QYpIo1ze8fYsWwY7h1T32pkv2DU+wKDuMt2BRa3PXFPwahtYsVkNVFdJiJlVVSIuZVFVhpRZJM9AiArSIAC0iQIsI0CICtIgALSJAiwjQIgK0iAAtIkCLCGTkUZ1Mw7pRcRLZqWIGww05FuVBt7/FHcNiY8Fw/b1FkbEQFr0NweVy73e/y1zyPgyGGwqMRV9/Yl9DcLPcl57yR3U3YDDc8P15UfrYbAge7NJ86cdXH0wlJZX3JU0Gw/X3Y1EN3a8ZglsNwcPfXpDxnE2ovK9oNBiuC5wXPUHFl7ch+IbFuaVzwnM2ofK+oNlguD7EYqgh+NaMqsNp3aTy8mk3GK7LzKjOnUaoIbh4rf3NG58NjveUeZXBcMMhd/3+huBa3oHIV9kXtLHzKoPhhnbzqFWVR4uZVFUeLWZSVXn1WiTNQIsI0CICtIgALSJAiwjQIgK0iAAtIkCLCNAiArSIAC0ikPcpsbN8iuH+yf/UP+DDBDtM6/nU2h9JPaaYOHI6Tt+c+JAabtfOl0Y5gQMO3HjfTDY7yfGDi4kjq2/4YO2nGrp+EJkifzBcPa9LV/Gpe7j582bH5kUqZ5fyB07kpD24yfGDi4kkr/u7/Cf1vN7fJhkWCoY7LTntP614nDcqmFTkN6jntbtdA9PpKjl+cDGxZPbwN29YNdwer0C+T+px0mPOn07C6g+ba9opdRlS9SbHjy0mlkyLS4x6/sU99G4wfDXC3AG3fE1HynQaKrIgVvrSlxw/s5ggud+nMb9J5dvTzKjrYPiuxc8WkqbTUJEF+dSzlRw/rZgg2d+Kop7X7jl+9m2xGAqG71qclgxJ02moyC9wA+xm7olIjrdncd4xMcmsYvxWMHzXomxDHc8RVzd2B2zU+0VP9F2cFwPB8H2L6Y8whor8EnFS9wbV27d4JGlXpxNMpWpdlUVzEZgALWpdi8XpDJr2/OIELWrNzzQwoEUEaBEBWkSAFhGgRQRoEQFaRIAWEaBFBGgRAVpEgBYRoEUEaBGBfYtLxrAqWJWEFktCi2mwKknYomgKutW792RYlY/Usejp4X/ij0m1tFDVeXBGLQktpsGqJLxfRIAWEaBFBGgRAVpEgBYRoEUEaBEBWkSAFhGgRQRoEYH/yfs0Jl4efpkAAAAASUVORK5CYII=" alt="" />

可以发现,这个结果与未索引english列之前的不同,它是排序的,原因正式如上所述。

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