（SQL 语句）声明自增元素

create TABLE PersonalUsers(

P_id int identity(0,1), //identity(0,1)用于说明P_id是自增的，且起始为0，增量为1

P_username nvarchar(50),

P_password nvarchar(50),

P_realName nvarchar(50),

P_idNum nvarchar(50),

P_phoneNum nvarchar(50),

P_address nvarchar(MAX),

P_gender nvarchar(50),

P_marriage nvarchar(50),

P_registered datetime,

primary key (P_id)  //声明主键为P_id

)