Question

我必须从某个表中删除数据，所以我使用以下查询：

delete from table_a 
where objectname in 
    (Select object_name from table_b where resolved='Y');

现在Select object_name from table_b where resolved='Y'查询将返回超过400万条记录，因此需要花费大量时间来执行。我试图以更具成本效益的方式编写它。

DELETE FROM table_a 
WHERE EXISTS ( SELECT 1 FROM table_b WHERE object_name= objectname AND RESOLVED = ‘Y’ )
AND ROWNUM < 10000;

但似乎有错误：

SQL错误：ORA-00911：无效字符00911. 00000 - “无效字符”*原因：标识符不能以字母和数字以外的任何ASCII字符开头。第一个字符后也允许$＃_。双引号括起来的标识符可以包含除doublequote之外的任何字符。替代引号（q'＃...＃'）不能使用空格，制表符或回车符作为分隔符。对于所有其他上下文，请参阅SQL语言参考手册。

请帮忙！

Answer 1

假设你有

table_a
table_b上引用table_a且设置为ON DELETE CASCADE或ON DELETE SET NULL的外键

您可以使用内联视图：

create table table_a as (select distinct object_name from all_objects);
alter table table_a add constraint pk_a primary key (object_name);

create table table_b as (
  select 
    distinct object_name, 
    (case when object_name like 'A%' then 'Y' else 'N' end)   as resolved
    from table_a);    
alter table table_b add constraint fk_b_a foreign key (object_name) 
  references table_a(object_name) on delete cascade;

delete from (
  select b.resolved 
  from table_a a 
  join table_b b on a.object_name = b.object_name)
where resolved = 'Y';

但老实说，EXISTS / IN方法更清晰，更容易理解。

通过以经济有效的方式连接两个表来删除查询

1 个答案: