学习:
http://www.cnblogs.com/huanghai223/archive/2011/06/29/2093660.html
declare
v_count integer := 0;
begin
select count(1) into v_count from user_constraints where constraint_name = 'SYS_C008270';
if (v_count > 0) then
--prd
execute immediate 'alter table tfz_grade_detail_rec_his drop constraint SYS_C008270';
else
--stg
execute immediate 'alter table tfz_grade_detail_rec_his drop constraint SYS_C008170';
end if;
end;