在PL/SQL里面使用if语句的时候，记得是elsif而不是elseif：

if...elsif...elsif....end if

学习案例如下：

declare

  region        varchar2(100) := '&region';--声明region的字符变量且默认标签为region

  country_count number := 0;               --声明country_count的数值变量

begin

  if upper(region) = 'EUROPE' then

    select count(*) into country_count from countries where region_id = 1;

    dbms_output.put_line('There are ' || country_count ||

                         ' countries in  the Europe region.');

  elsif upper(region) = 'AMERICAS' then

    select count(*) into country_count from countries where region_id = 2;

    dbms_output.put_line('There are ' || country_count ||

                         ' countries in  the Americas region.');

  elsif upper(region) = 'ASIA' then

    select count(*) into country_count from countries where region_id = 3;

    dbms_output.put_line('There are ' || country_count ||

                         ' countries in  the ASIA region.');   

  elsif upper(region) = 'MIDDLE EAST AND AFRICA' then

    select count(*) into country_count from countries where region_id = 4;

    dbms_output.put_line('There are ' || country_count ||

                         ' countries in  the middle East and Africa region.');   

  else

    dbms_output.put_line('You have entered an invaid region ,please try again');

  end if;

  end;