sql基础

查看数据库: show databases;

查看是否已经选定数据库: select database();

选择数据库: use databaseName;

创建数据库: create database databaseName;

删除数据库: drop database databaseName;

查看存储引擎: show engines

查询

查询语句: select * from tableName;

查询不同的列: select distinct id from tableName;

限制返回的条数: select * from tableName limit 5;

(如果需要定义开始的行数)

select * from tableName limit 6,5

 

排序

普通排序: select * from tableName order by id;

多个列排序: select * from tableName order by id,name;

(顺序是按照输出时列的顺序进行排序)

指定方向排序: select * from tableName order by id DESC ;

(DESC是降序排序，默认情况下是升序排序的)

指定方向多个列排序: select * from tableName order by id DESC ,name;

 

过滤

where字句: select * from tableName where name='test';

范围检查:select * from tableName where name between 5 and 6;

空值检查: select * from tableName where name is NULL;

AND字句: select * from tableName where id=1 and name='test';

OR字句: select * from tableName where id=1 or name='test';

(如果通知存在and和or字句，会优先执行and，所以必要时候可用括号对其进行限制)

IN字句: select * from tableName where id in (100,200);

NOT字句: select * from tableName where id not in (100,200);

LIKE字句:(%:任意数量的任意字符，_:单个任意字符)

select * from tableName where name like 'test%';

select * from tableName where name like 'test_';

 

正则

基本字符匹配: select * from tableName where name REGEXP '100 tom';

(REGEXP后跟的是正则表达式)

 

计算字段

拼接字符串: select concat(name,'(',id,')') from tableName;

算叔计算: select id ,name ,number ,price,num from tableName;

 

数据处理函数

RTrim()/LTrim():清楚左/右侧空白

soundex():返回串的soundex值

locate():找出串的一个字符

lower():全部转成小写

upper():全部转成大写

subString():返回子串的字符

left()/right():返回串的左/右边字符

 

日期处理函数

addDate():增加一个日期

addtime():增加一个时间

curDate():返回当前日期

curTime():返回当前时间

Date():返回日期部分

DateDiff():计算两个日期之差

Date_Add():日期运算

Date_Formate():格式化日期

Day():返回日期的天数部分

DayOfWeek():返回该日期是周几

Hour():返回小时

Minute():返回分钟

Month():返回小时

Now():返回当前时间

Second():返回秒

Time():返回时间

year():返回年份

 

聚集函数

AVG():返回某列的平均值

select AVG(number) as avg_number from tableName;

COUNT():返回某列的行数

select count(*) from tablieName;

select count(number) from tableName;

MAX():返回某列的最大值

select max(number) as min_number from tableName;

MIN():返回某列的最小值

select min(number) as min_number from tableName;

SUM():返回某列之和

select sum(number) as sum_number from tableName;

(以上这几个函数可以在同一sql中使用)

 

分组

普通分组:

select vend_id,count(*) as num_prods from tableName group by vend_id;

过滤分组:

select cust_id,count(*) as orders from tableName group by cust_id having count(*)>=2;

(having是对分组进行过滤，where是对查询进行过滤)

分组排序

select order_num,sum(quantity*item_price) as ordertotal from tableName

group by order_num having sum(quantity*item_price) >= 50

order by ordertotal;

 

子查询

select cust_id from orders where order_num in (select order_num from orderitems where prod_id = 'test2');

select cust_name,cust_state,(select count(*) from orders where orders.cust_id=customers.cust_id) as orders form customers order by cust_name;

 

联结

自联结:

select vend_name,prod_name,prod_price from vendors,products

where vendors.vend_id = products.vend_id order by vend_name,prod_name;

内联:

select vend_id,prod_name,prod_price from vendors inner join products

on vendors.vend_id = products.vend_id;

外联:

select customers.id,orders.order_num from customers left outer join orders

on customers.cust_id = orders.cust_id;

select customers.cust_id,orders.order_num from customers right outer join orders

on orders.cust_id = customers.cust_id;

 

插入

整行插入

insert into tableName values (1,'test','123');

insert into tableName (id,name,password) values (1,'test','123');

插入检索出的数据

insert into tableName1 (id,name,password) 

 

更新数据:

update tableName set cust_email = 'elmer@fudd.com' where cust_id = 10005;

 

删除数据:

delete from tableName where cust_id = 10006;

 

创建表

create table tableName(

cust_id int not null auto_increment,

cust_name char(50) not null,

cust_address char(50) null,

cust_city char(50) null,

cust_check char(10) not null default 1,

primary ley(cust_id)

)engine = innoDB;

primary ley=>指定主键

auto_increment=>自增

default=>默认值

engine=>指定引擎

注:MySQL有三种引擎：

innoDB:可靠的事务引擎，不能全文搜索

memory:类似于innoDB,数据存放于内存中，相应比较快

MyIsAM:极高的性能引擎，支持全文搜索，单不支持事务处理

 

更新表

alter table tableName add vend_phone char(50);//增加字段

alter table tableName drop column vend_phone;//删除字段

 

删除表

drop table tableName;

 

重命名表

rename table tableName1 to tableName2;

 

视图

创建视图

create procedure productpring()

begin

    select avg(prod_price) as priceaverage from products;

end;

调用存储过程

call productpring();

删除存储过程

drop procedure productpring();

带参数的存储过程

create procedure productpring(

out pl decimal(8,2),

out ph decimal(8,2),

out pa decimal(8,2))

begin

    select Min(prod_price) into pl from products;

    select Max(prod_price) into ph from products;

    select Avg(prod_price) into pa from products;

end;

out=>指定相应参数，用于存放值返回给调用者

in=>传递给存储过程

变量

call productpring(@pricelow,@pricehight,@priceaverage);

select @pricelow;//查询返回值

 

触发器

创建触发器

create trigger newproduct after install on products

for each row select 'product added';

after each=>在插入语句成功后触发

for each=>对每一条出入语句都执行

select 'product added'=>在成功后触发显示'product added'

删除触发器

drop trigger newproduct ;