日期：2015-06-28 00:00:00 来源: IT猫扑网
一、select语法
SELECT
[ALL | DISTINCT | DISTINCTROW ]
[HIGH_PRIORITY]
[STRAIGHT_JOIN]
[SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
[SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]
select_expr [, select_expr ...]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[PROCEDURE procedure_name(argument_list)]
[INTO OUTFILE 'file_name'
[CHARACTER SET charset_name]
export_options
| INTO DUMPFILE 'file_name'
| INTO var_name [, var_name]]
[FOR UPDATE | LOCK IN SHARE MODE]]
简化一下语法如下：
select column1，column2，...
from table1，table2，...
[where condition]
[group by …]
[having …]
[order by …]
1、例如：下面例子
mysql> create table jokes(
-> id int unsigned not null auto_increment primary key,
-> joketext text,
-> jokedate date
-> )engine=myisam charset=utf8;
mysql> insert into jokes values('','why not?',now());
#计算列（select 用于检索从一个或多个表中选取出的行。Select也可以被用于检索没有引用任何表的计算列）
select 1+1 as total; //结果为2
+-------+
| total |
+-------+
| 2 |
+-------+
#从表Jokes中挑选所有的东西
select * from jokes;
+----+----------+------------+
| id | joketext | jokedate |
+----+----------+------------+
| 1 | why not? | 2010-04-08 |
+----+----------+------------+
#选择感兴趣的列(投影)
select id, jokedate from jokes;
#我们是不是可以多少显示一点笑话正文的内容呢？(预览)
mysql> select id,left(joketext,3) as content,jokedate from jokes;
+----+---------+------------+
| id | content | jokedate |
+----+---------+------------+
| 1 | why | 2010-04-08 |
+----+---------+------------+
#统计表中记录数
mysql> select count(*) as records from jokes;
+---------+
| records |
+---------+
| 1 |
+---------+
#统计2000年1月1日之后录入的笑话记录数
select count(*) from jokes where jokedate >= ‘2000-01-01’;
#笑话里包含"鞋" //%表示任一字符
mysql> select joketext as content from jokes where joketext like '%not%';
+----------+
| content |
+----------+
| why not? |
+----------+
#显示2000年4月份的包含"鞋"的笑话(组合查询)
select joketext from where joketext like "%not%" and jokedate >= "2000-04-01" and jokedate < "2000-05-1";
2、分组语句
员工表emp(empno, name, tel, deptno, sal)
部门表dept(deptno, dname, addr)
1）显示每个部门的最高工资
select deptno, max(sal) from emp group by deptno;
select deptno,max(sal) as ‘最高工资’ from emp group by deptno;
注意：max()、min()…函数在显示列中出现时，必须与group by一起使用
3、嵌套子查询
1）显示每个部门收入最高的职工信息。
select * from emp
where sal in ( select max(sal) from emp
group by deptno );(先按组排序，后显示一组中最大的)
2）按照工资高低显示职工信息
select * from emp order by sal desc;
3）limit s,n
limit子句可以被用于强制select语句返回指定的记录数。limit接受一个或两个数字参数。参数必须是一个整数常量。如果给定两个参数，第一个参数指定第一个返回记录行的偏移量，第二参数指定返回记录行的最大数目n。初始记录行的偏移量是0(而不是1)。
（1）查看薪水最低的前5位员工信息
select * from emp order by sal limit 0,5;
óselect * from emp order by sal limit 5;
（2）查看第3到第7号员工信息
select * from emp limit 2,5;
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