DML 触发器2

create or replace trigger GenerateAuthorId
    before insert on or update on Authors
    for each row
begin
    select author_sequence.nextval
    into :new.ID    --：new.ID表示触发完成后，要插入的值. 就是说将 -1改为nextval
    from dual;
end GenerateAuthorId;
/

insert into authors(ID,first_name,last_name)
vaules(-1,‘David‘,‘Zheng‘);

create or replace trigger TempDelede
    before delete on temp_table
    for each row
declare
    v_TempRec temp_table%rowtype
begin
    v_TempRec:=old;  --错误赋值，会编译报错
    v_TempRec.char_col:=:old.char_col;  --正确赋值
    v_TempRec.num_col:=:old.num_col;    --正确赋值
end TempDelede;
/

create or replace trigger GenerateAuthorId
    before insert on or update on Authors
    referencing new as new_author     --都不带冒号
    for each row
begin
    select author_sequence.nextval
    into :new_author.ID    --带冒号
    from dual;
end GenerateAuthorId;
/

create or replace trigger CheckPrice
    before insert or update  of price on books
    for each row
    when  (new.price>500.00)  --new没加冒号
begin
    DBMS_OUTPUT.PUT_LINE(‘price is higher than 500‘);
end CheckPrice;
/

create table inventory_audit(
    change_type char(1) not null, 
    change_by varchar2(8) not null,
    timestramp date not null,
    old_isbn char(10),
    new_isbn char(10),
    old_status varchar(25),
    new_status varchar(25),
    old_amount varchar(25),
    new_amount varchar(25)
    );   ---创建 inventory_audit


create or replace LogInventoryChanges
    before insert or update or delete on inventory
    for each row
declare
    v_ChangeType char(1);
begin
    if inserting then v_ChangeType=‘I‘  --用I表示Insert
    elsif updating then v_ChangeType=‘U‘
    else v_ChangeType=‘D‘
    insert into inventory_audit(    --将改变的状态插入到inventory_audit表中
        change_type,change_by,timestamp,
        old_isbn,new_isbn,old_status,new_status,old_amount,new_amount
        )
    vaules(
        v_ChangeType,user,sysdate,
        :old.isbn,:new.isbn,:old.status,:new.status,:old.amount,:new.amount
        )
end LogInventoryChanges;
/