一、SQL高级语句

1.1 SELECT

显示表格中一个或数个栏位的所有资料

语法：SELECT "栏位" FROM "表名";

实例：查询表中的name一列

select "name" from class1;

1.2 DISTINCT

不显示重复的资料

语法：SELECT DISTINCT "栏位" FROM "表名";
SELECT DISTINCT Store_Name FROM Store_Info;

1.3 WHERE

有条件查询

语法：SELECT "栏位" FROM "表名" WHERE "条件";

实例：

select name from football where value > 60000000;

1.4 AND OR

代表且、或、和的意思

语法：SELECT "栏位" FROM "表名" WHERE "条件1" {[AND|OR] "条件2"}+ ;
示例：

select name from football where value > 60000000 or (value >30000000 and value < 60000000);

1.5 IN ----显示已知的值的资料

语法：SELECT "栏位" FROM "表名" WHERE "栏位" IN ('值1', '值2', ...);

实例：

select name from football where name in ('梅西','C罗');

1.6 BETWEEN

显示两个值范围内的资料

语法：SELECT "栏位" FROM "表名" WHERE "栏位" BETWEEN '值1' AND '值2';

示例：

select name from football where age between '20' and '30';

1.7 通配符

通常通配符都是跟 LIKE 一起使用的

 

1.8 LIKE

匹配一个模式来找出我们要的资料

语法：SELECT "栏位" FROM "表名" WHERE "栏位" LIKE {模式};

示例1：

select name from football where value like '8%';

示例2：

select name from football where age like '2_';

示例3：

select name from football where value like '%000';

1.9 ORDER BY

按关键字排序

语法：SELECT "栏位" FROM "表名" [WHERE "条件"] ORDER BY "栏位" [ASC, DESC];

#ASC 是按照升序进行排序的，是默认的排序方式。
#DESC 是按降序方式进行排序。

实例1：

select name,value from football order by value desc;

实例2：

select name,age,value from football order by age asc;

二、SQL函数

2.1 数学函数：

select abs(-10),rand(),mod(10,3),power(2,10),round(3.1415);

 

select round(3.1415926,3),sqrt(9),truncate(3.1415926,3),ceil(3.5),floor(1.11),greatest(1,2,3,4),least(1,2,3,4); 

2.2 聚合函数：

实例1：计算平均身价

select avg(value) from football;

实例2：计算身价的非null个数

select count(value) from football where value is not null;
select count(distinct value) from football;

select count(*) from football;

 

实例3：

select max(value) from football;		#最高值
select min(value) from football;		#最低值
select sum(value) from football;		#总和

2.3 字符串函数：

 

实例1：trim()

select trim(' abc ');

实例2：concat(x,y)

select concat(name,value) from football where id=1;
select name || value from football where id=1;
#如sql_mode开启 了PIPES_AS_CONCAT， "||" 视为字符串的连接操作符而非或运算符，和字符串的拼接函数Concat相类似，这和Oracle数据库使用方法一-

可以添加分隔符

select name || ':' || value from football where id=1;

实例3：substr(x,y) 和 substr(x,y,z)

select substr(value,4) from football where name='内马尔'; #value的第4位开始的字符
select substr(value,1,2) from football where name='内马尔'; #value的第1位开始的2位字符

实例4：length(x)

select length(value) from football where id =5;
select name,value,length(value) from football; # 显示value的长度并显示name和value

实例5：replace(x,y,z)

select name,value,replace(value,0,9) from football;

实例6：upper(x) 和 lower(x)

select name,upper(name) from football where id=7;
select name,lower(name) from football where id=7;

实例7：left(x,y)和 right(x,y)

select name,left(name,5) from football where id=7;
select name,right(name,3) from football where id=7;

实例8：repeat(x,y)

select id,name,repeat(id,5) from football where id=7;

实例9：space(x)、strcmp(x,y)和reverse(x)

2.4 GROUP BY

对GROUP BY后面的栏位的查询结果进行汇总分组，通常是结合聚合函数一起使用的 GROUP BY 有一个原则，就是 SELECT
后面的所有列中，没有使用聚合函数的列，必须出现在GROUP BY后面。

语法：SELECT "栏位1", SUM("栏位2") FROM "表名" GROUP BY "栏位1";
示例：

select name,sum(value) from football group by name;
select name,sum(value) from football group by name order by value desc;

2.5 HAVING

用来过滤由GROUP BY语句返回的记录集，通常与GROUP BY语句联合使用
HAVING语句的存在弥补了WHERE关键字不能与聚合函数联合使用的不足。如果被SELECT的只有函数栏，那就不需要GROUP BY子句。

语法：SELECT "栏位1", SUM("栏位2") FROM "表格名" GROUP BY "栏位1" HAVING (函数条件);

示例：

select name,sum(value) from football group by name having sum(value) > 80000000;

2.6 别名

栏位別名 表格別名

语法：SELECT "表格別名"."栏位1" [AS] "栏位別名" FROM "表格名" [AS] "表格別名";

示例：

select f.area,sum(value) "total value" from football f group by f.area;

2.7 连接查询

建立两张表，字段数据如下，后面测试用：

1）inner join(等值相连)

只返回两个表中联结字段相等的行

SELECT * FROM club A INNER JOIN football B on A.name = B.name;

2）left join(左联接)

返回包括左表中的所有记录和右表中联结字段相等的记录

SELECT * FROM club A LEFT JOIN football B on A.name = B.name;

3）right join(右联接)

返回包括右表中的所有记录和左表中联结字段相等的记录

SELECT * FROM club A RIGHT JOIN football B on A.name = B.name;

2.8 子查询

连接表格，在WHERE 子句或HAVING 子句中插入另一个SQL语句

语法：SELECT "栏位1" FROM "表格1" WHERE "栏位2" [比较运算符] #外查询
(SELECT "栏位1" FROM "表格1" WHERE "条件"); #内查询
示例：

SELECT SUM(value) FROM football WHERE name IN (SELECT name FROM club WHERE club = '皇家马德里');