1、if 语句：
if 条件表达式1 then 语句块1;[elseif 条件表达式2 then 语句块2;]...[else 语句块n;]end if;
例如：输入角色，学号，查询名字；
delimiter $$create function get_name_fn1(no char(11), role char(10)) returns char(10)begin declare name char(10); if role = "student" then select student_name into name from student where student_no = no; elseif role = "teacher" then select teacher_name into name from teacher where teacher_no = no; else set name = "输入错误"; end if; return name;end;$$delimiter ;#--测试：select get_name_fn1("2023002", "student");select get_name_fn1("001","teacher");select get_name_fn1("007","teacher");select get_name_fn1("2023004","stu");2、case语句：
case 表达式 when value1 then 语句块1; when value2 then 语句块2; when value3 then 语句块3; ... else 语句块n;end case;
例如，输入日期，查询周几；
delimiter $$create function get_week_fn(d date) returns char(20)begin declare week char(20); case weekday(d) when 0 then set week = "星期一"; when 1 then set week = "星期二"; when 2 then set week = "星期三"; when 3 then set week = "星期四"; when 4 then set week = "星期五"; else set week = "休息"; end case; return week;end;$$delimiter ;
3、循环语句：
while、repeat、loop；MySQL还提供了iterate语句和leave语句，用于循环的内部控制；
(相关资料图)
[循环标签:]while 条件表达式 do 循环体;end while [循环标签];
例如:实现求和函数，1到n
delimiter $$create function get_sum_fn(n int) returns intbegin declare sum int; declare cur int; set sum = 0; set cur = 1; while cur <= n do set sum = sum + cur; set cur = cur + 1; end while; return sum;end;$$delimiter ;#--测试：select get_sum_fn(10);select get_sum_fn(0);select get_sum_fn(100);
3.1、leave语句：用于提前退出循环语句；相当于break语句；
leave 循环标签;
我们设置此while为死循环，当内部if条件成立就退出；
delimiter $$create function get_sum1_fn(n int) returns intbegin declare sum int; declare cur int; set sum = 0; set cur = 1; add_sum: while true do set sum = sum + cur; if cur = n then leave add_sum; end if; set cur = cur + 1; end while add_sum; return sum;end;$$delimiter ;
3.2、iterate语句：用于跳出本次循环继续下次循环；相当于continue语句；
iterate 循环标签;
例如，我们将1~10之间的偶数相加；
delimiter $$create function get_sum2_fn(n int) returns intbegin declare sum int; declare cur int; set sum = 0; set cur = 0; add_sum : while cur <= n do set cur = cur + 1; if cur%2 = 1 then iterate add_sum; end if; set sum = cur + sum; end while add_sum; return sum;end;$$
4、repeat语句：
当表达式值为false时，反复执行循环，直到条件表达式为true；
[循环标签:]repeat 循环体： until 条件表达式end repeat[循环标签];
同样我们实现相加；注意until后的条件表达式没有结束符；
delimiter $$create function get_sum3_fn(n int) returns intbegin declare sum int default 0; declare cur int default 0; repeat set cur = cur + 1; set sum = sum + cur; until cur = n end repeat; return sum;end;$$delimiter ;
5、loop语句：
loop循环语句本身没有停止循环的语句，因此loop本身通常借助leave语句跳出loop循环；
[循环标签:] loop 循环体; if 条件表达式 then leave 循环标签; end if;end loop [循环标签];
还是实现相加：
delimiter $$create function get_sum4_fn(n int) returns intbegin declare sum int default 0; declare cur int default 0; add_sum: loop set cur = cur + 1; set sum = sum + cur; if cur = n then leave add_sum; end if; end loop add_sum; return sum;end;$$;delimiter ;
总结：五种控制流程语句，查看创建函数；
show function status like "%\_fn"\G
