DDL在PLSQL不能直接使用，需要添加EXECUTE IMMEDIATE ，EXECUTE IMMEDIATE 'DROP TABLE IF EXISTS table_a;' ; EXECUTE IMMEDIATE 'CREATE TABLE IF NOT EXISTS table_a AS
selec * from table_b
where b.dt='||yes_d||';';

DDL语句请用动态SQL语法
execute immediate 'create table xxx';

declare 
    yes_d        date :=add_days(curdate(), -1);
    befyse_d     date :=add_days(curdate(),-2);
    yes_d_last_m date :=add_months(yes_d,-1);
    start_m      date := add_days(yes_d, - DAY (yes_d) + 1);
    yes_d_30d    date :=add_days(curdate(),-31);
    start_last_m date :=add_months(start_m,-1);
begin
   execute immediate 'DROP TABLE IF EXISTS table_a;';     
   execute immediate 'CREATE TABLE /*IF NOT EXISTS*/ table_a AS select * from table_b b where b.dt = :B1' using yes_d; 
end;