在同一张表上插入触发器后更新 [英] Update with after insert trigger on same table

问题描述

我有一个要在tableA上编写插入触发器的操作.它将使用相同的表但不同的列执行更新.执行此操作时出现错误.我的触发器是

I have a to write a insert trigger on a tableA. which will perform update with same table but different column. I am getting error while doing this. My trigger is

create or replace trigger trigger_A
after insert on table_A
begin
  update table_A set col1=1 where col1 is null;
end;

我有一个应用程序，它将单独执行col2并将col1保持为空.因此，一旦插入行，我的触发器将为col1提供值.但是插入行时出现错误消息，提示触发器失败且无效". 这该怎么做. TIA.

I have an application will perform col2 alone will be inserted and col1 will be kept null. so my trigger will give value for col1 once the row is inserted. But i am getting error saying "Trigger is failed and invalid" when a row is inserted. How to do this. TIA.

推荐答案

如果要分配简单的默认值，最简单的方法是使用DEFAULT子句在表上声明它.

If you want to assign a simple default value, the easiest way is to declare it on the table, using the DEFAULT clause.

SQL> create table t42
  2    ( col1 number default 1 not null
  3      , col2 date)
  4  /

Table created.

SQL> insert into t42 (col2) values (sysdate)
  2  /

1 row created.

SQL> select * from t42
  2  /

      COL1 COL2
---------- ---------
         1 03-AUG-11

SQL>

这适用于文字或伪列，例如SYSDATE或USER.如果要使用用户定义的函数或序列派生更复杂的值，则需要使用 触发器.

This works with literals or pseudocolumns such as SYSDATE or USER. If you want to derive a more complicated value with a user-defined function or a sequence, you will need to use a trigger.

这是表格的新版本...

Here is a new version of the table...

SQL> create table t42
  2    ( col1 number default 1 not null
  3      , col2 date default sysdate
  4      , col3 varchar2(30) default user
  5      , col4 number )
  6  /

Table created.

SQL>

...带有触发器:

SQL> create or replace trigger t42_trg
  2      before insert or update
  3      on t42
  4      for each row
  5  begin
  6      if :new.col4 is null
  7      then
  8          :new.col4 := my_seq.nextval;
  9      end if;
 10  end;
 11  /

Trigger created.

SQL> insert into t42 (col1, col2, col3)
  2  values (99, sysdate, 'MR KNOX')
  3  /

1 row created.

SQL> select * from t42
  2  /

      COL1 COL2      COL3                                 COL4
---------- --------- ------------------------------ ----------
        99 03-AUG-11 MR KNOX                               161

SQL>

请注意，尽管表上的每一列都是默认值，但我必须至少填充一列以使SQL有效:

Note that although every column on the table is defaultable, I have to populate at least one column to make the SQL valid:

SQL> insert into t42 values ()
  2  /
insert into t42 values ()
                        *
ERROR at line 1:
ORA-00936: missing expression


SQL>

但是我可以将NULL传递给COL4以获得完全默认的记录:

But I can pass in NULL to COL4 to get a completely defaulted record:

SQL> insert into t42 (col4) values (null)
  2  /

1 row created.

SQL> select * from t42
  2  /

      COL1 COL2      COL3                                 COL4
---------- --------- ------------------------------ ----------
        99 03-AUG-11 MR KNOX                               161
         1 03-AUG-11 APC                                   162

SQL>

---

Caveat Lector:我的触发器使用了新的11g语法.在以前的版本中，我们必须使用SELECT语句分配序列值:

---

Caveat lector: my trigger uses the new 11g syntax. In previous versions we have to assign the sequence value using a SELECT statement:

select my_seq.nextval
into :new.col4
from dual;

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