单表查询
单表查询的语法
不带关键字的语法
1 2 3 4 5 6 | select { 1. * | 2. 字段名| 3. 四则运行| 4. 聚合函数} from 表名 [where 条件] 1. * 表示查询所有字段 2. 可以手动要查询的字段 3. 字段的值可以进行加减乘除运算 4. 聚合函数,用于统计 where 是可选的 |
field()函数
可以用来对SQL中查询结果集进行指定顺序排序。
函数使用格式如下:order by (str,str1,str2,str3,str4……),str与str1,str2,str3,str4比较,其中str指的是字段名字,意为:字段str按照字符串str1,str2,str3,str4的顺序返回查询到的结果集。
如果表中str字段值不存在于str1,str2,str3,str4中的记录,放在结果集最前面返回。
带关键字的语法
1 2 3 4 5 6 | SELECT 字段 1 ,字段 2. .. FROM 表名 WHERE 条件 GROUP BY field HAVING 筛选 ORDER BY field LIMIT 限制条数 |
关键字的执行优先级
mysql查询时的书写顺序
1 | select..distinct..字段名... from ...where...group by...having...order by...limit.. |
mysql查询时的执行顺序
1 2 3 4 5 6 7 8 9 | 重点中的重点:关键字的执行优先级 from where group by having select distinct order by limit |
1.找到表:from
2.拿着where指定的约束条件,去文件/表中取出一条条记录
3.将取出的一条条记录进行分组group by,如果没有group by,则整体作为一组
4.将分组的结果进行having过滤
5.执行select,查看结果集中的哪个列,或列的计算结果
6.去重复
7.将结果按条件排序:order by
8.限制结果的显示条数
需要注意的点
1 2 | from 后面的表关联,是自右向左解析的 而where条件的解析顺序是自下而上的。 也就是说,在写SQL文的时候,尽量把数据量小的表放在最右边来进行关联(用小表去匹配大表), 而把能筛选出小量数据的条件放在where语句的最左边 (用小表去匹配大表) |
简单查询
准备表和记录
company.employee 员工id id int 姓名 emp_name varchar 性别 sex enum 年龄 age int 入职日期 hire_date date 岗位 post varchar 职位描述 post_comment varchar 薪水 salary double 办公室 office int 部门编号 depart_id int 创建表 create table employee( id int not null unique auto_increment, name varchar(20) not null, sex enum('male','female') not null default 'male', #大部分是男的 age int(3) unsigned not null default 28, hire_date date not null, post varchar(50), post_comment varchar(100), salary double(15,2), #双精度浮点数(非准确小数值),参数15是数字总个数,2是小数点后个数 office int, #一个部门一个屋子 depart_id int ); #查看表结构 mysql> desc employee; +--------------+-----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------------+-----------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(20) | NO | | NULL | | | sex | enum('male','female') | NO | | male | | | age | int(3) unsigned | NO | | 28 | | | hire_date | date | NO | | NULL | | | post | varchar(50) | YES | | NULL | | | post_comment | varchar(100) | YES | | NULL | | | salary | double(15,2) | YES | | NULL | | | office | int(11) | YES | | NULL | | | depart_id | int(11) | YES | | NULL | | +--------------+-----------------------+------+-----+---------+----------------+ 插入记录 三个部门:教学,销售,运营 insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values ('xiong1','male',18,'20170301','外交大使',7300.33,401,1), #以下是教学部 ('xiong2','male',78,'20150302','teacher',1000000.31,401,1), ('xiong3','male',81,'20130305','teacher',8300,401,1), ('xiong4','male',73,'20140701','teacher',3500,401,1), ('xiong5','male',28,'20121101','teacher',2100,401,1), ('xiong6','female',18,'20110211','teacher',9000,401,1), ('xiong7','male',18,'19000301','teacher',30000,401,1), ('xiong8','male',48,'20101111','teacher',10000,401,1), ('dog1','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门 ('dog2','female',38,'20101101','sale',2000.35,402,2), ('dog3','female',18,'20110312','sale',1000.37,402,2), ('dog4','female',18,'20160513','sale',3000.29,402,2), ('dog5','female',28,'20170127','sale',4000.33,402,2), ('miao1','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门 ('miao2','male',18,'19970312','operation',20000,403,3), ('miao3','female',18,'20130311','operation',19000,403,3), ('miao4','male',18,'20150411','operation',18000,403,3), ('miao5','female',18,'20140512','operation',17000,403,3) ; ps:如果在windows系统中,插入中文字符,select的结果为空白,可以将所有字符编码统一设置成gbk
简单查询
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | 简单查询 select id ,name,sex,age,hire_date,post,post_comment,salary,office,depart_id from employee; select * from employee; select name,salary from employee; 避免重复distinct select distinct post from employee; 通过四则运算查询 select name, salary * 12 from employee; select name, salary * 12 as Annual_salary from employee; select name, salary * 12 Annual_salary from employee; 定义显示格式 <br> concat() 函数用于连接字符串 写法一<br> select concat( '姓名: ' ,name, ' 年薪: ' , salary * 12 ) as Annual_salary from employee; 写法二<br> select concat( '姓名: ' ,name) as 姓名,concat( '年薪: ' ,salary) as 年薪 from employee; #注意逗号不能敲成中文的<br><br> CONCAT_WS() 第一个参数为分隔符, SELECT CONCAT_WS( ':' ,name,salary * 12 ) AS Annual_salary FROM employee;<br> 结合CASE语句: SELECT ( CASE WHEN NAME = 'xiong1' THEN NAME WHEN NAME = 'xiong2' THEN CONCAT(name, '_BIGSB' ) ELSE concat(NAME, 'SB' ) END ) as new_name FROM emp; |
补充:case when语句的详细分析
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 | case when语句,用于计算条件列表并返回多个可能结果表达式之一。 CASE 具有两种格式:简单 CASE 函数将某个表达式与一组简单表达式进行比较以确定结果。<br> CASE 搜索函数计算一组布尔表达式以确定结果。 两种格式都支持可选的 ELSE 参数 简单的case函数 CASE input_expression WHEN when_expression THEN result_expression [...n ] [ ELSE else_result_expression END 参数介绍: input_expression是使用简单 CASE 格式时所计算的表达式。Input_expression 是任何有效的 Microsoft SQL Server 表达式。 WHEN when_expression使用简单 CASE 格式时 input_expression 所比较的简单表达式。When_expression 是任意有效的 SQL Server 表达式。Input_expression 和每个 when_expression 的数据类型必须相同,或者是隐性转换。 占位符,表明可以使用多个 WHEN when_expression THEN result_expression 子句或 WHEN Boolean_expression THEN result_expression 子句。 THEN result_expression 当 input_expression = when_expression 取值为 TRUE,或者 Boolean_expression 取值 TRUE 时返回的表达式。 result expression 是任意有效的 SQL Server 表达式。 ELSE else_result_expression当比较运算取值不为 TRUE 时返回的表达式。如果省略此参数并且比较运算取值不为 TRUE,CASE 将返回 NULL 值。else_result_expression 是任意有效的 SQL Server 表达式。else_result_expression 和所有 result_expression 的数据类型必须相同,或者必须是隐性转换。 1 简单 CASE 函数:返回结果值介绍: 计算 input_expression,然后按指定顺序对每个 WHEN 子句的 input_expression = when_expression 进行计算。 返回第一个取值为 TRUE 的 (input_expression = when_expression) 的 result_expression。如果没有取值为 TRUE 的 input_expression = when_expression,则当指定 ELSE 子句时 SQL Server 将返回 else_result_expression;若没有指定 ELSE 子句,则返回 NULL 值。 2 CASE 搜索函数 CASE WHEN Boolean_expression THEN result_expression [...n ] [ ELSE else_result_expression END 参数介绍: WHEN Boolean_expression 使用 CASE 搜索格式时所计算的布尔表达式。Boolean_expression 是任意有效的布尔表达式。结果类型从 result_expressions 和可选 else_result_expression 的类型集合中返回最高的优先规则类型。有关更多信息,请参见数据类型的优先顺序。 CASE 搜索函数:返回结果值介绍: 按指定顺序为每个 WHEN 子句的 Boolean_expression 求值。返回第一个取值为 TRUE 的 Boolean_expression 的 result_expression。 如果没有取值为 TRUE 的 Boolean_expression,则当指定 ELSE 子句时 SQL Server 将返回 else_result_expression;若没有指定 ELSE 子句,则返回 NULL 值。 3 、CASE 可能是 SQL 中被误用最多的关键字之一 虽然,可能以前用过这个关键字来创建字段,但是它还具有更多用法。 例如,可以在 WHERE 子句中使用 CASE。或者在 GROUP BY 子句中使用 CASE 使用CASE WHEN进行字符串替换处理,稍加深入,还可以得到以前认为不可能得到的分组排序结果集 4 其他 简单语句 多重语句 在SELECT查询中使用CASE WHEN |
练习
1 2 3 4 | 1 查出所有员工的名字,薪资,格式为 <名字:egon> <薪资: 3000 > 2 查出所有的岗位(去掉重复) 3 查出所有员工名字,以及他们的年薪,年薪的字段名为annual_year |
1 2 3 | select concat( '<名字:' ,name, '> ' , '<薪资:' ,salary, '>' ) from employee; select distinct depart_id from employee; select name,salary * 12 annual_salary from employee; |
WHERE约束
where字句中可以使用:
1. 比较运算符:> < >= <= <> !=
2. between 80 and 100 值在10到20之间
3. in(80,90,100) 值是10或20或30
4. like 'egon%'
pattern可以是%或_,
%表示任意多字符
_表示一个字符
select name from employee where name like 'xiong%';
5. 逻辑运算符:在多个条件直接可以使用逻辑运算符 and or not
regex
any
all
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 | 1 :单条件查询 SELECT name FROM employee WHERE post = 'sale' ; 2 :多条件查询 SELECT name,salary FROM employee WHERE post = 'teacher' AND salary> 10000 ; 3 :关键字BETWEEN AND SELECT name,salary FROM employee WHERE salary BETWEEN 10000 AND 20000 ; SELECT name,salary FROM employee WHERE salary NOT BETWEEN 10000 AND 20000 ; 4 :关键字IS NULL(判断某个字段是否为NULL不能用等号,需要用IS) SELECT name,post_comment FROM employee WHERE post_comment IS NULL; SELECT name,post_comment FROM employee WHERE post_comment IS NOT NULL; SELECT name,post_comment FROM employee WHERE post_comment = ' '; 注意' '是空字符串,不是null ps: 执行 update employee set post_comment = '' where id = 2 ; 再用上条查看,就会有结果了 5 :关键字IN集合查询 SELECT name,salary FROM employee WHERE salary = 3000 OR salary = 3500 OR salary = 4000 OR salary = 9000 ; SELECT name,salary FROM employee WHERE salary IN ( 3000 , 3500 , 4000 , 9000 ) ; SELECT name,salary FROM employee WHERE salary NOT IN ( 3000 , 3500 , 4000 , 9000 ) ; 6 :关键字like模糊查询 通配符’ % ’ SELECT * FROM employee WHERE name LIKE 'eg%' ; 通配符’_’ SELECT * FROM employee WHERE name LIKE 'al__' ; |
练习
1. 查看岗位是teacher的员工姓名、年龄 2. 查看岗位是teacher且年龄大于 30 岁的员工姓名、年龄 3. 查看岗位是teacher且薪资在 9000 - 1000 范围内的员工姓名、年龄、薪资 4. 查看岗位描述不为NULL的员工信息 5. 查看岗位是teacher且薪资是 10000 或 9000 或 30000 的员工姓名、年龄、薪资 6. 查看岗位是teacher且薪资不是 10000 或 9000 或 30000 的员工姓名、年龄、薪资 7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪 |
1 2 3 4 5 6 7 | select name,age from employee where post = 'teacher' ; select name,age from employee where post = 'teacher' and age > 30 ; select name,age,salary from employee where post = 'teacher' and salary between 9000 and 10000 ; select * from employee where post_comment is not null; select name,age,salary from employee where post = 'teacher' and salary in ( 10000 , 9000 , 30000 ); select name,age,salary from employee where post = 'teacher' and salary not in ( 10000 , 9000 , 30000 ); select name,salary * 12 from employee where post = 'teacher' and name like 'jin%' ; |
分组查询:GROUP BY
什么是分组,为什么要分组?
1 2 3 4 5 6 7 8 9 10 11 12 | 1 、首先明确一点:分组发生在where之后,即分组是基于where之后得到的记录而进行的 2 、分组指的是:将所有记录按照某个 相同字段 进行归类,比如针对员工信息表的职位分组, 或者按照性别进行分组等 3 、为何要分组呢?<br> 数据库中分组是为了统计 <br> 取每个部门的最高工资 取每个部门的员工数 取男人数和女人数 小窍门:‘每’这个字后面的字段,就是我们分组的依据也即重复性比较高的字段 4 、大前提: 可以按照任意字段分组,但是分组完毕后,比如group by post,只能查看post字段,其他都被隐藏了 如果想查看组内信息,需要借助于聚合函数!!! |
ONLY_FULL GROUP_BY
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | #查看MySQL 5.7默认的sql_mode如下: mysql> select @@ global .sql_mode; ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE, NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER, NO_ENGINE_SUBSTITUTION #!!!注意 ONLY_FULL_GROUP_BY的语义就是确定select target list 中的所有列的值都是明确语义, 简单的说来,在ONLY_FULL_GROUP_BY模式下,target list 中的值要么是来自于聚集函数的结果, 要么是来自于group by list 中的表达式的值。 #设置sql_mole如下操作(我们可以去掉ONLY_FULL_GROUP_BY模式): mysql> set global sql_mode = 'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'; !!!SQL_MODE设置!!! |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 | mysql> select @@ global .sql_mode; + - - - - - - - - - - - - - - - - - - - + | @@ global .sql_mode | + - - - - - - - - - - - - - - - - - - - + | | + - - - - - - - - - - - - - - - - - - - + row in set ( 0.00 sec) mysql> select * from emp group by post; + - - - - + - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id | + - - - - + - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | 14 | miao1 | male | 28 | 2016 - 03 - 11 | operation | NULL | 10000.13 | 403 | 3 | | 9 | dog1 | female | 48 | 2015 - 03 - 11 | sale | NULL | 3000.13 | 402 | 2 | | 2 | xiong2 | male | 78 | 2015 - 03 - 02 | teacher | NULL | 1000000.31 | 401 | 1 | | 1 | xiong1 | male | 18 | 2017 - 03 - 01 | 外交大使 | NULL | 7300.33 | 401 | 1 | + - - - - + - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + 4 rows in set ( 0.00 sec) #由于没有设置ONLY_FULL_GROUP_BY,于是也可以有结果,默认都是组内的第一条记录,但其实这是没有意义的 mysql> set global sql_mode = 'ONLY_FULL_GROUP_BY' ; Query OK, 0 rows affected ( 0.00 sec) mysql> quit #设置成功后,一定要退出,然后重新登录方可生效 Bye mysql> use db1; Database changed mysql> select * from emp group by post; #报错 ERROR 1055 ( 42000 ): 'db1.emp.id' isn't in GROUP BY mysql> select post,count( id ) from emp group by post; #只能查看分组依据和使用聚合函数 + - - - - - - - - - - - + - - - - - - - - - - - + | post | count( id ) | + - - - - - - - - - - - + - - - - - - - - - - - + | operation | 5 | | sale | 5 | | teacher | 7 | | 外交大使 | 1 | + - - - - - - - - - - - + - - - - - - - - - - - + 4 rows in set ( 0.03 sec) |
GROUP BY
应该注意的一些点
1 2 3 4 5 6 7 8 9 10 11 12 13 | 单独使用GROUP BY关键字分组 SELECT post FROM employee GROUP BY post; 注意:我们按照post字段分组,那么select查询的字段只能是post, 想要获取组内的其他相关信息,需要借助函数 GROUP BY关键字和GROUP_CONCAT()函数一起使用 使用了GROUP_CONCAT()之后,就可以看到组内所有的记录,但是这条记录是默认用逗号拼接而成的 SELECT post,GROUP_CONCAT(name) FROM employee GROUP BY post; #按照岗位分组,并查看组内成员名 SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post; GROUP BY与聚合函数一起使用 select post,count( id ) as count from employee group by post; #按照岗位分组,并查看每个组有多少人 |
1 2 3 4 5 | 强调: 如果我们用unique的字段作为分组的依据,则每一条记录自成一组,这种分组没有意义 多条记录之间的某个字段值相同,该字段通常用来作为分组的依据 |
聚合函数
1 2 3 4 5 6 7 8 9 10 | 强调:聚合函数聚合的是组的内容,若是没有分组,则默认一组 示例: SELECT COUNT( * ) FROM employee; SELECT COUNT( * ) FROM employee WHERE depart_id = 1 ; SELECT MAX (salary) FROM employee; SELECT MIN (salary) FROM employee; SELECT AVG(salary) FROM employee; SELECT SUM (salary) FROM employee; SELECT SUM (salary) FROM employee WHERE depart_id = 3 ; |
练习
1 2 3 4 5 6 7 | 1. 查询岗位名以及岗位包含的所有员工名字 2. 查询岗位名以及各岗位内包含的员工个数 3. 查询公司内男员工和女员工的个数 4. 查询岗位名以及各岗位的平均薪资 5. 查询岗位名以及各岗位的最高薪资 6. 查询岗位名以及各岗位的最低薪资 7. 查询男员工与男员工的平均薪资,女员工与女员工的平均薪资 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 | 题 1 :分组 mysql> select post,group_concat(name) from employee group by post; + - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + | post | group_concat(name) | + - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + | operation | miao1,miao2,miao3,miao4,miao5 | | sale | dog1,dog2,dog3,dog4,dog5 | | teacher | xiong2,xiong3,xiong4,xiong5,xiong6,xiong7,xiong8 | | 外交大使 | xiong1 | + - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + 4 rows in set ( 0.00 sec) 题目 2 : mysql> select post,count( id ) from employee group by post; + - - - - - - - - - - - + - - - - - - - - - - - + | post | count( id ) | + - - - - - - - - - - - + - - - - - - - - - - - + | operation | 5 | | sale | 5 | | teacher | 7 | | 外交大使 | 1 | + - - - - - - - - - - - + - - - - - - - - - - - + 4 rows in set ( 0.00 sec) 题目 3 : mysql> select sex,count( id ) from employee group by sex; + - - - - - - - - + - - - - - - - - - - - + | sex | count( id ) | + - - - - - - - - + - - - - - - - - - - - + | male | 10 | | female | 8 | + - - - - - - - - + - - - - - - - - - - - + 2 rows in set ( 0.00 sec) 题目 4 : mysql> select post,avg(salary) from employee group by post; + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | post | avg(salary) | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | operation | 16800.026000 | | sale | 2600.294000 | | teacher | 151842.901429 | | 外交大使 | 7300.330000 | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + 4 rows in set ( 0.00 sec) 题目 5 mysql> select post, max (salary) from employee group by post; + - - - - - - - - - - - + - - - - - - - - - - - - - + | post | max (salary) | + - - - - - - - - - - - + - - - - - - - - - - - - - + | operation | 20000.00 | | sale | 4000.33 | | teacher | 1000000.31 | | 外交大使 | 7300.33 | + - - - - - - - - - - - + - - - - - - - - - - - - - + 4 rows in set ( 0.04 sec) 题目 6 mysql> select post, min (salary) from employee group by post; + - - - - - - - - - - - + - - - - - - - - - - - - - + | post | min (salary) | + - - - - - - - - - - - + - - - - - - - - - - - - - + | operation | 10000.13 | | sale | 1000.37 | | teacher | 2100.00 | | 外交大使 | 7300.33 | + - - - - - - - - - - - + - - - - - - - - - - - - - + 4 rows in set ( 0.00 sec) 题目七 mysql> select sex,avg(salary) from employee group by sex; + - - - - - - - - + - - - - - - - - - - - - - - - + | sex | avg(salary) | + - - - - - - - - + - - - - - - - - - - - - - - - + | male | 110920.077000 | | female | 7250.183750 | + - - - - - - - - + - - - - - - - - - - - - - - - + |
HAVING过滤
HAVING与WHERE不一样的地方在于
1 2 3 | 执行优先级从高到低:where > group by > having 1. Where 发生在分组group by之前,因而Where中可以有任意字段,但是绝对不能使用聚合函数。 2. Having发生在分组group by之后,因而Having中可以使用分组的字段,无法直接取到其他字段,可以使用聚合函数 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | mysql> select @@sql_mode; + - - - - - - - - - - - - - - - - - - - - + | @@sql_mode | + - - - - - - - - - - - - - - - - - - - - + | ONLY_FULL_GROUP_BY | + - - - - - - - - - - - - - - - - - - - - + 1 row in set ( 0.00 sec) mysql> select * from emp where salary > 100000 ; + - - - - + - - - - - - + - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id | + - - - - + - - - - - - + - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | 2 | alex | male | 78 | 2015 - 03 - 02 | teacher | NULL | 1000000.31 | 401 | 1 | + - - - - + - - - - - - + - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + 1 row in set ( 0.00 sec) mysql> select * from emp having salary > 100000 ; ERROR 1463 ( 42000 ): Non - grouping field 'salary' is used in HAVING clause mysql> select post,group_concat(name) from emp group by post having salary > 10000 ; #错误,分组后无法直接取到salary字段 ERROR 1054 ( 42S22 ): Unknown column 'salary' in 'having clause' mysql> select post,group_concat(name) from employee group by post having avg(salary) > 10000 ; + - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + | post | group_concat(name) | + - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + | operation | miao1,miao2,miao3,miao4,miao5 | | teacher | xiong2,xiong3,xiong4,xiong5,xiong6,xiong7,xiong8 | + - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + 2 rows in set ( 0.00 sec) |
小练习
1 2 3 | 1. 查询各岗位内包含的员工个数小于 2 的岗位名、岗位内包含员工名字、个数 3. 查询各岗位平均薪资大于 10000 的岗位名、平均工资 4. 查询各岗位平均薪资大于 10000 且小于 20000 的岗位名、平均工资 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | 题目 1 : mysql> select post,group_concat(name),count( id ) from employee group by post having count( id ) < 2 ; + - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - + | post | group_concat(name) | count( id ) | + - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - + | 外交大使 | xiong1 | 1 | + - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - + 1 row in set ( 0.00 sec) 题目 2 : mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 ; + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | post | avg(salary) | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | operation | 16800.026000 | | teacher | 151842.901429 | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + 题目 3 : mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) < 20000 ; + - - - - - - - - - - - + - - - - - - - - - - - - - - + | post | avg(salary) | + - - - - - - - - - - - + - - - - - - - - - - - - - - + | operation | 16800.026000 | + - - - - - - - - - - - + - - - - - - - - - - - - - - + |
查询排序:ORDER BY
按单列排序
SELECT * FROM employee ORDER BY salary;
SELECT * FROM employee ORDER BY salary ASC;
SELECT * FROM employee ORDER BY salary DESC;
按多列排序:先按照age排序,如果年纪相同,则按照薪资排序
SELECT * from employee
ORDER BY age,
salary DESC;
补充
1 2 | 用 DESC 表示按倒序排序(即:从大到小排序) ---降序排列 用 ACS 表示按正序排序(即:从小到大排序)---升序排列 |
小练习
1 2 3 | 1. 查询所有员工信息,先按照age升序排序,如果age相同则按照hire_date降序排序 2. 查询各岗位平均薪资大于 10000 的岗位名、平均工资,结果按平均薪资升序排列 3. 查询各岗位平均薪资大于 10000 的岗位名、平均工资,结果按平均薪资降序排列 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | #题目1 mysql> select * from employee ORDER BY age asc,hire_date desc; #题目2 mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc; + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | post | avg(salary) | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | operation | 16800.026000 | | teacher | 151842.901429 | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + #题目3 mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc; + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | post | avg(salary) | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + | teacher | 151842.901429 | | operation | 16800.026000 | + - - - - - - - - - - - + - - - - - - - - - - - - - - - + |
限制查询的记录数:LIMIT
1 2 3 4 5 6 7 8 | SELECT * FROM employee ORDER BY salary DESC LIMIT 3 ; #默认初始位置为0,读三条记录 SELECT * FROM employee ORDER BY salary DESC LIMIT 0 , 5 ; #从第0开始,即先查询出第一条,然后包含这一条在内往后查5条 SELECT * FROM employee ORDER BY salary DESC LIMIT 5 , 5 ; #从第5开始,即先查询出第6条,然后包含这一条在内往后查5条 |
小练习
分页显示,每页5条
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 | mysql> select * from employee limit 0 , 5 ; + - - - - + - - - - - - - - - - - + - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id | + - - - - + - - - - - - - - - - - + - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | 1 | egon | male | 18 | 2017 - 03 - 01 | 老男孩驻沙河办事处外交大使 | NULL | 7300.33 | 401 | 1 | | 2 | alex | male | 78 | 2015 - 03 - 02 | teacher | | 1000000.31 | 401 | 1 | | 3 | wupeiqi | male | 81 | 2013 - 03 - 05 | teacher | NULL | 8300.00 | 401 | 1 | | 4 | yuanhao | male | 73 | 2014 - 07 - 01 | teacher | NULL | 3500.00 | 401 | 1 | | 5 | liwenzhou | male | 28 | 2012 - 11 - 01 | teacher | NULL | 2100.00 | 401 | 1 | + - - - - + - - - - - - - - - - - + - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + 5 rows in set ( 0.00 sec) mysql> select * from employee limit 5 , 5 ; + - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id | + - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | 6 | jingliyang | female | 18 | 2011 - 02 - 11 | teacher | NULL | 9000.00 | 401 | 1 | | 7 | jinxin | male | 18 | 1900 - 03 - 01 | teacher | NULL | 30000.00 | 401 | 1 | | 8 | 成龙 | male | 48 | 2010 - 11 - 11 | teacher | NULL | 10000.00 | 401 | 1 | | 9 | 歪歪 | female | 48 | 2015 - 03 - 11 | sale | NULL | 3000.13 | 402 | 2 | | 10 | 丫丫 | female | 38 | 2010 - 11 - 01 | sale | NULL | 2000.35 | 402 | 2 | + - - - - + - - - - - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + 5 rows in set ( 0.00 sec) mysql> select * from employee limit 10 , 5 ; + - - - - + - - - - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id | + - - - - + - - - - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + | 11 | 丁丁 | female | 18 | 2011 - 03 - 12 | sale | NULL | 1000.37 | 402 | 2 | | 12 | 星星 | female | 18 | 2016 - 05 - 13 | sale | NULL | 3000.29 | 402 | 2 | | 13 | 格格 | female | 28 | 2017 - 01 - 27 | sale | NULL | 4000.33 | 402 | 2 | | 14 | 张野 | male | 28 | 2016 - 03 - 11 | operation | NULL | 10000.13 | 403 | 3 | | 15 | 程咬金 | male | 18 | 1997 - 03 - 12 | operation | NULL | 20000.00 | 403 | 3 | + - - - - + - - - - - - - - - - - + - - - - - - - - + - - - - - + - - - - - - - - - - - - + - - - - - - - - - - - + - - - - - - - - - - - - - - + - - - - - - - - - - + - - - - - - - - + - - - - - - - - - - - + 5 rows in set ( 0.00 sec) |
使用正则表达式查询
1 2 3 4 5 6 7 8 | SELECT * FROM employee WHERE name REGEXP '^ale' ; SELECT * FROM employee WHERE name REGEXP 'on$' ; SELECT * FROM employee WHERE name REGEXP 'm{2}' ; 小结:对字符串匹配的方式 WHERE name = 'egon' ; WHERE name LIKE 'yua%' ; WHERE name REGEXP 'on$' ; |
小练习
查看所有员工中名字是jin开头,n或者g结果的员工信息
1 | select * from employee where name regexp '^jin.*[gn]$' ; |
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