oracle数据库在级联和触发时遇到删除错误

Question

我在数据库中有两个表，一个是PS_POST，一个是PS_STAR。

这里是有DDL：

-------------------------------------------------------- 
-- DDL for Table PS_POST 
-------------------------------------------------------- 

    CREATE TABLE "C##STY"."PS_POST" 
    ( "POST_ID" NUMBER GENERATED ALWAYS AS IDENTITY MINVALUE 1 MAXVALUE 9999999999999999999999999999 INCREMENT BY 1 START WITH 1 CACHE 20 NOORDER NOCYCLE , 
    "USER_ID" NUMBER, 
    "GROUP_ID" NUMBER DEFAULT 0, 
    "TIME" DATE, 
    "TITLE" VARCHAR2(200 BYTE) DEFAULT 'Default_title', 
    "STAR_NUMBER" NUMBER DEFAULT 0, 
    "CONTENT" VARCHAR2(4000 BYTE) DEFAULT 'Default_content' 
    ) ; 
-------------------------------------------------------- 
-- DDL for Index POST_PK 
-------------------------------------------------------- 

    CREATE UNIQUE INDEX "C##STY"."POST_PK" ON "C##STY"."PS_POST" ("POST_ID") ; 
-------------------------------------------------------- 
-- Constraints for Table PS_POST 
-------------------------------------------------------- 

    ALTER TABLE "C##STY"."PS_POST" MODIFY ("USER_ID" NOT NULL ENABLE); 
    ALTER TABLE "C##STY"."PS_POST" ADD CONSTRAINT "POST_PK" PRIMARY KEY ("POST_ID") 
    ENABLE; 
    ALTER TABLE "C##STY"."PS_POST" MODIFY ("POST_ID" NOT NULL ENABLE); 



-------------------------------------------------------- 
-- DDL for Table PS_STAR 
-------------------------------------------------------- 

    CREATE TABLE "C##STY"."PS_STAR" 
    ( "USER_ID" NUMBER, 
    "POST_ID" NUMBER, 
    "TIME" DATE 
    ) ; 
-------------------------------------------------------- 
-- DDL for Index STAR_PK 
-------------------------------------------------------- 

    CREATE UNIQUE INDEX "C##STY"."STAR_PK" ON "C##STY"."PS_STAR" ("USER_ID", "POST_ID") 
    ; 
-------------------------------------------------------- 
-- DDL for Trigger STAR_TRIGGER 
-------------------------------------------------------- 

    CREATE OR REPLACE EDITIONABLE TRIGGER "C##STY"."STAR_TRIGGER" after insert on PS_STAR 
referencing new as new old as old 
for each row 
begin 
update PS_POST 
set 
STAR_NUMBER = STAR_NUMBER + 1 
where POST_ID = :new.POST_ID; 

end; 
/
ALTER TRIGGER "C##STY"."STAR_TRIGGER" ENABLE; 
-------------------------------------------------------- 
-- DDL for Trigger STAR_DELETE_TRIGGER 
-------------------------------------------------------- 

    CREATE OR REPLACE EDITIONABLE TRIGGER "C##STY"."STAR_DELETE_TRIGGER" before delete on PS_STAR 
referencing new as new old as old 
for each row 
begin 
update PS_POST 
set 
STAR_NUMBER = STAR_NUMBER - 1 
where POST_ID = :old.POST_ID; 

end; 
/
ALTER TRIGGER "C##STY"."STAR_DELETE_TRIGGER" ENABLE; 
-------------------------------------------------------- 
-- Constraints for Table PS_STAR 
-------------------------------------------------------- 

    ALTER TABLE "C##STY"."PS_STAR" ADD CONSTRAINT "STAR_PK" PRIMARY KEY ("USER_ID", "POST_ID") 
    ENABLE; 
    ALTER TABLE "C##STY"."PS_STAR" MODIFY ("POST_ID" NOT NULL ENABLE); 
    ALTER TABLE "C##STY"."PS_STAR" MODIFY ("USER_ID" NOT NULL ENABLE); 

所以我设置PS_STAR当帖子被删除被级联删除。我还有一个触发器，用于在删除星形记录时更新PS_POST表中的STAR_NUMBER。当我尝试删除PS_POST中的某个项目时，似乎PS_STAR中的触发器无法正常工作，并且出现错误：

ORA-04091: C##STY.PS_POST is mutating, trigger/function may not see it 

如何解决此问题？提前致谢。

Answer 1

可能最好的方案是从PS_POST表中删除非规范化的 STAR_NUMBER列，并删除触发器 - 只需要计算PS_STAR记录的数量即可。除非在一些极端情况下，否则“表现非规范化”很少有理由。

但是，如果您确实需要保留它，则需要防止触发器在从中删除记录时尝试更新PS_POST表。这可以通过使用一个包在里面，而实现与一个全局变量是这样的：

create or replace package ps_post_pkg is 
    deleting_post boolean default false; 
end; 

然后添加两个声明 - 电平触发到PS_POST：

create or replace trigger ps_post_before_delete_stmt 
before delete on ps_post 
begin 
    ps_post_pkg.deleting_post := true; 
end; 

create or replace trigger ps_post_after_delete_stmt 
after delete on ps_post 
begin 
    ps_post_pkg.deleting_post := false; 
end; 

现在修改你START_DELETE_TRIGGER的身体：

begin 
    if not ps_post_pkg.deleting_post then 
    update PS_POST 
    set STAR_NUMBER = STAR_NUMBER - 1 
    where POST_ID = :old.POST_ID; 
    end if; 
end; 

现在，当记录从PO_POST中删除时，删除将级联到PS_STAR，但START_DELETE_TRIGGER将n不要尝试更新刚删除的PS_POST记录。