Mysql学习笔记（七）mysql编程基础之自定义函数。

delimiter $$
create function fn_liangzifunction() returns int
no sql
begin
    set @row_no = @row_no + 1;
    return @row_no;
end;
$$
delimiter ;

delimiter $$
create function fn_get_name(student_num int) returns char(50)
reads sql data
begin
    declare student_names char(50);
    select student_name into student_names from student where student_no = student_num;
    return student_names;
    end;
$$
delimiter ;

#将查询结果赋予变量。

delimiter $$
create function fn_get_choose_count(student_no1 int) returns int(50)
reads sql data
begin
    declare choose_num int(50);
    select count(*) into choose_num from choose where student_no = student_no1;
    return choose_num;
end;
$$
delimiter ;

delimiter $$
create function fn_get_name(no int,role char(50)) returns char(50)
reads sql data
begin
    declare name char(50);
    if('student'=role) then
        select student_name into name from student where student_no=no;
    elseif('teacher'=role) then
        select teacher_name into name from teacher where teacher_no=no;
    else set name = '输入有误';
    end if;
    return name;
end;
$$
delimiter ;

#if else
delimiter  $$
create function fn_get_name(no int,role char(20)) returns char(20)
reads sql data
begin
    declare name char(20);
    if(role='student') then
        select student_name into name from student where student_no=no;
    elseif(role='teacher') then
        select teacher_name into name from teacher where teacher_no=no;
    else set name='输入错误';
    end if;
    return name;
end;
$$
delimiter ;

#switch case

delimiter $$
create function fn_get_week(week_no int) returns char(20)
no sql
begin
    declare week char(20);
    case week_no
        when 0 then set week = '星期一';
        when 1 then set week = '星期二';
        when 2 then set week = '星期三';
        when 3 then set week = '星期四';
        when 4 then set week = '星期五';
        else set week = '今天休息';
    end case;
    return week;
end;
$$
delimiter ;

#根据现在的时间判断问候语

delimiter $$
create function fn_get_hello(time int) returns char(20)
no sql
begin
    declare hello char(20);
    if(time < 9) then
        set hello = '早上好';
    elseif( 9 < time and time <= 12) then
        set hello = '上午好';
    elseif( 12 < time and time <= 18) then
        set hello = '下午好';
    elseif(18 < time and time < 22)   then
        set hello = '晚上好';
    else
        set hello = '晚安';
    end if;
    return hello;
end;
$$
delimiter ;

#练习switch case 语句

delimiter $$
create function fn_get_myweek(day int) returns char(50)
no sql
begin
    declare weekname char(50);
    case day
        when 1 then set weekname = '星期一';
        when 2 then set weekname = '星期2';
        when 3 then set weekname = '星期3';
        when 4 then set weekname = '星期4';
        when 5 then set weekname = '星期5';
        else set weekname = '星期日';
    end case;
    return weekname;
end;
$$
delimiter ;

#while语句
#和其他编程一样，当条件表达式值为true时，就一直执行循环体，直到条件表达式为false。

delimiter $$
create function fn_get_mysum(num int) returns int
no sql
begin
    declare sum int default 0;
    declare start int default 0;
    while start < num do
        set start = start + 1;
        set sum   = sum   + start;
    end while;
    return sum;
end;
$$
delimiter ; 

#while中的内部控制语句
#leave   相当于php循环中的break了。
# 至于下面的add_num,相当于给while的循环起一个名字。

delimiter $$
create function fn_get_sum1(n int) returns int
no sql
begin
    declare sum   int  default 0;
    declare start int  default 0;
    add_num : while true do
        set start = start + 1;
        set sum   = sum   + start;
        if(start = n) then
          leave add_num;
        end if;
    end while add_num;
    return sum;
end;
$$
delimiter;