--基本查询
select * from pet

--列出指定的列
select name, owner form pet

--直接进行算术运算，对字段起别名
select sin(1+2) as sin

--where条件
select * from pet where (birth>'1980' and species='dog') or species='bird'

--对null的条件
select * from pet where sex is not null

--所有名字第四位是n的宠物信息是
select * from pet where owner like '___n%'


--所有主人名叫gwen或benny的宠物
select * from pet where owner in ('gwen' , 'benny')

--查询出生日期在90年代是宠物，相当与   >= and  <=
select * from pet where birth between '1990' and '1999'

--按主人姓名排序，相同的按宠物姓名倒序排列
select * from pet order by owner, name desc

--查询性别为公的宠物，按生日倒序排列
select * from pet where sex='m' order by birth desc

--char_length()返回的字符的长度，length()返回字节长度
SELECT owner,length(owner),char_length(owner) FROM pet p;



--列出养有宠物狗的人名
select distinct owner from pet where species='dog'

--用两种方法查询出所有狗和猫的名字、出生年份、出生月份
select name, left(birth,4) as year, mid(birth, 6, 2) as month from pet 
where species='dog' or species='cat'

select name, year(birth) as year, month(birth) as month from pet 
where species in('dog','cat')

--查询所有名字中存在字母'e'的人，将他们养的宠物按类别、年龄排序
select name, species, birth 
from pet 
where owner like '%e%'
order by species,birth desc

--数字函数
select round(2.345,2), truncate(2.345,2), mod(323,5)

--日期函数
select now(), curdate(), curtime()

select adddate('2007-02-02', interval 31 day)

--求出所有宠物的年龄
select name,birth,
truncate(datediff(now(),birth)/365,0) as age1,
year(now())-year(birth) - (dayofyear(birth)>dayofyear(now())) as age2
from pet

--分组函数
select min(birth),max(birth),avg(birth),count(*),count(sex),
sum(birth)
from pet

--每种宠物各有几只
select species,count(*)
from pet
group by species

--查询年龄最大的宠物的信息
select * from pet where birth =
      (select max(birth) from pet)

--每年各出生了几只宠物
select year(birth), count(*) from pet group by year(birth)

--鸟和猫的性别比例
select species, sex, count(*)
from pet
where species in ('cat','bird')
group by species, sex

--各种宠物年龄的和
select species, sum(truncate(datediff(now(),birth)/365,0)) as SumAge
from pet
group by species

--数量大于1的宠物种类
select species, count(*) as c
from pet
group by species
having c>=2

--基本双表关联
select a.name,a.species, a.sex,b.date, b.type, b.remark
from pet a,event b
where a.name = b.name

--查询宠物产仔时的年龄
select a.name, a.species,
   truncate(datediff(b.date,a.birth)/365,0) as age
from pet a,event b
where a.name = b.name and b.type='litter'

--90年代出生的狗的事件列表
select a.name,birth,species,sex,date,type,remark
from pet a,event b
where a.name=b.name and birth between '1990' and '1999'
and species='dog'

--活着的宠物按发生的事件类型分组，看各种事件发生的次数
select type, count(*)
from pet a, event b
where a.name=b.name and a.death is null
group by type

--记录的事件数量超过1条的宠物信息
select a.name,species,sex,count(*)
from pet a, event b
where a.name = b.name
group by b.name
having count(*)>=2

--列出发生了两件事情的宠物的事件记录信息
select a.name,type,date,remark,b.species,b.sex,b.owner
from event a, pet b
where a.name=b.name and
  b.name in
  (
    select name
    from event
    group by name
    having count(*)=2
  )


--插入语句
insert into pet (name,species,birth)
values ('KKK','snake','2007-01-01');

insert into pet
values ('KK','Diane','cat','f',null,null);

insert into pet set name='k',owner='Benny'


--更新语句
update pet set species='snake',sex='f',birth=now()
where name='k'

--将事件表中生日的日期，更新到pet表中相应宠物的birth字段
update pet a
set birth = (
              select date
              from event b
              where a.name=b.name and b.type='birthday'
            )
where a.name in (
                  select name
                  from event
                  where type='birthday'
                )


--删除语句
delete from pet where name like 'k%'