select * from T_Debt
–检索T_Debt表返回所有的数据,负载大

select FNumber,FPerson from T_Debt
–检索T_Debt表仅返回FPerson字段列,负载小

select FNumber as 编码 from T_Debt
select FNumber 编码 from T_Debt
–检索T_Debt表返回FNumber字段列并把FNumber列名显示为’编码’,AS语法可省略

select * from T_Debt where FNumber='002'
–根据条件检索T_Debt表仅返回FNumber字段等于’002′的数据

select * from T_Debt where FNumber='002' or FPerson='zerg'
–根据条件检索T_Debt表仅返回FNumber字段或者FPerson字段满足条件

数据汇总函数：
max() 计算字段最大值
min() 计算字段最小值
avg() 计算字段平均值
sum() 计算字段合计值
count() 统计数据条数

select max(FAmount) from T_Debt
–检索T_Debt表返回FAmount字段最大值,返回的数据列为虚拟列

select count(*) from T_Debt
select count(FAmount) from T_Debt
–如果FAmount字段所有数据总没有NULL空值，则上述2句语句效果相同，如果FAmount字段包含NULL空值，则count(*)结果大于count(FAmount)结果

select * from T_Debt order by FNumber/升序排列,无参默认
select * from T_Debt order by FNumber desc/降序排列
–检索T_Debt表返回结果根据FNumber字段排列

select * from T_Debt where FPerson like 'k%'
select * from T_Debt where FPerson like '_e___'
–检索T_Debt表返回FPerson字段,模糊过滤

select * from T_Debt where FPerson like '[kz]%'
select * from T_Debt where FPerson like 'k%' or FPerson like 'z%'
——————————————————————-
select * from T_Debt where FPerson like '[^kz]%'
select * from T_Debt where not(FPerson like 'k%') and not(FPerson like 'z%')
–检索T_Debt表返回FPerson字段，上述2种语句效果相同

select * from T_Debt where FPerson is null
select * from T_Debt where FPerson is not null
–空值检测，使用is，而不是’=’

select fitemid from t_ICItem union select fitemid from ICInventory
–联合2张表去除重复记录
select fitemid from t_ICItem union all select fitemid from ICInventory
–联合2张表不去除重复记录
select fitemid from t_ICItem intersect select fitemid from ICInventory
–联合2张表仅显示重复记录
select fitemid from t_ICItem t1 where t1.fitemid not in (select fitemid from ICInventory)
–联合2张表仅显示不在ICInventory中的记录

create table T_Person (FName varchar(20),FAge int,FRemark varchar(20),primary key (FName))
–创建T_Person表，FName为主键
create table T_Debt (FNumber varchar(20),FAmount numeric(10,2) not null,FPerson varchar(20),primary key (FNumber),foreign key (FPerson) references T_Person(FName))
–创建T_Debt表，FNumber为主键，FAmount字段非空控制，T_Person表FName字段与T_Debt表FNumber字段为外键关联

insert into T_Person(FName,FAge,fremark) values('kevin','25','jiangsu')
–向T-Person表插入一笔数据
insert into T_Debt(fnumber,famount,fperson) values('001','5000.00','kevin')
–向T_Debt表插入一笔数据，FPerson字段外键约束自T_Person表FName字段(即FPerson字段想插入的数据kevin必须预先存在于T_Person表FName字段中)

update T_Person set fage='24',FRemark='shanghai' where FName='zerg'
–更新T_Person表FAge、FRemark字段

delete from T_Debt where FNumber='001'
–删除T_Debt表中FNumber字段为001的数据

drop table T_Debt
drop talbe T_Person
–删除T_Debt、T_Person表