本篇文章主要讲述的是MySQL SELECT句法的简单分析，我们大家都知道MySQL数据库是我们大家经常使用的数据库，其相关的应用也是备受关注的，那么以下的文章主要是对MySQL SELECT句法的简单分析。
$sql="select * from article where id=1" 和 $sql="select * from article where id=1"，都可以得到正确的结果，但有时分开写或许能更明了一点，特别是当sql语句比较长时
可以用<code class="sql color1">in<code class="sql plain">来实现
<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain">$sql="select * from article where id in(1,3,5)"</code></code></code></code>
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain">3、使用concat连接查询的结果<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">$sql="select concat(id,"-",con) as res from article where id=1"</code></code></code></code></code></code></code>
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">返回"1-article content"<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">4、使用locate<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">用法：
<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">select locate("hello","hello baby");</code></code></code></code></code></code></code></code></code></code><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">存在返回1，不存在返回0<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">5、使用group by
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain">group by 是把相同的结果编为一组<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">exam：$sql="select city ,count(*) from customer group by city";</code></code></code></code></code></code></code></code></code></code></code></code></code>
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">这句话的意思就是从customer表里列出所有不重复的城市，及其数量（有点类似distinct）<br />
group by 经常与AVG(),MIN(),MAX(),SUM(),COUNT()一起使用
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">6、使用having<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">having 允许有条件地聚合数据为组
<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">$sql="select city,count(*),min(birth_day) from customer group by city having count(*)>10";</code></code></code></code></code></code></code></code></code></code></code></code></code>
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">这句话是先按city归组，然后找出city地数量大于10的城市<br />
btw：使用group by + having 速度有点慢<br />
同时having子句包含的表达式必须在之前出现过
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">7、组合子句
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">where、group by、having、order by（如果这四个都要使用的话，一般按这个顺序排列）
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">8、使用distinct<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">distinct是去掉重复值用的
<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">$sql="select distinct city from customer order by id desc";</code></code></code></code></code></code></code></code></code></code></code></code></code>
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">这句话的意思就是从customer表中查询所有的不重复的city
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">9、使用limit<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">如果要显示某条记录之后的所有记录
<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">$sql="select * from article limit 100,-1";</code></code></code></code></code></code></code></code></code></code></code></code></code>
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">10、多表查询
<code class="sql plain"><code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">$sql="select user_name from user u,member m where u.id=m.id and m.reg_date>=2015-08-13 order by u.id desc"</code></code></code></code></code></code></code></code></code></code></code></code></code>
<code class="sql color1"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql plain"><code class="sql string">注意：如果user和member两个标同时有user_name字段，会出现mysql错误（因为mysql不知道你到底要查询哪个表里的user_name），必须指明是哪个表的；
