select * from book where bdate<to_date('2000-1-15','yyyy-mm-dd hh24:mi:ss')
select max(salary) from emp group by typedeclare
str varchar2(20);
outcome varchar2(20);
begin
str:=to_char(&num);
for i in 1..length(str) loop
outcome:=substr(str,i,1)||outcome;
end loop;
dbms_output.put_line(outcome);
end;
select max(salary) from emp group by typedeclare
str varchar2(20);
outcome varchar2(20);
begin
str:=to_char(&num);
for i in 1..length(str) loop
outcome:=substr(str,i,1)||outcome;
end loop;
dbms_output.put_line(outcome);
end;
2.select 部门,工作类别,max(工资) from emp group by 部门,工作类别
3.左右反转---没理解