plsql中declare用法、number用法、字符串拼接用法（||），as关键字用法 声明时同时赋值 有大用 有大大用

declare：用于plsql中的声明变量，和begin连用，和存储过程结构相似

declare
   v_sal  number(7,2):=60000;----声明时同时赋值,声明变量v_sal 类型为number(7,2)前面的7表示总共允许7个字符长，称为宽度。后面2是保留小数点后面两位，称为精度。
   v_comm2 number(7,2):=v_sal*0.20;
   v_aa number(7,2):=100;
   v_message varchar2(255):='eligible for commission';
begin
   declare
         v_sal   number(7,2):=10;
         v_comm  number(7,2):=0;
         v_total_comp number(7,2):=v_sal+v_comm;
    begin
         v_message:='clerk not'||v_message;   
         v_comm:=v_sal*0.30;
         v_aa:=v_aa*0.30;
         DBMS_OUTPUT.PUT_LINE ('2:'||TO_CHAR(v_aa));--dbms_output.put_line 输出数据括号里的||代表字符串的拼接
         
         DBMS_OUTPUT.PUT_LINE ('1:'||TO_CHAR(v_comm2));
     end;
         v_message:='salesman'||v_message;
         DBMS_OUTPUT.PUT_LINE (TO_CHAR(v_comm2));
end;

select employee_ID as employees,first_name||last_name as "employee Name",Department_ID as "departement",salary as "Salary",email as "Email",phone_number as "phone",hire_date as "ehire date",job_id as "job Id" from employees;

select employee_ID  employees,first_name||last_name  "employee Name",Department_ID  "departement",salary  "Salary",email  "Email",phone_number  "phone",hire_date  "ehire date",job_id  "job Id" from employees;

以上两句都能实现以下效果，plsql中取别名最好不要用as，||符号是拼接字符串