oracle 选择变量时选择什么都不返回？答案

【问题标题】：oracle select into variable when select return nothing?oracle 选择变量时选择什么都不返回？
【发布时间】：2012-02-19 14:23:09
【问题描述】：

declare
 fName varchar2(255 char);
begin
 SELECT x.constraint_name into fName FROM all_constraints x
 JOIN all_cons_columns c ON
 c.table_name = x.table_name AND c.constraint_name = x.constraint_name
 WHERE x.table_name = 'MY_TABLE_NAME' AND x.constraint_type = 'R' AND c.column_name ='MY_COLUMN_NAME';
 if fName is not null THEN
  execute immediate 'alter table MY_TABLE_NAME drop constraint ' || fName;
 end if;

 SELECT x.constraint_name into fName FROM all_constraints x
 JOIN all_cons_columns c ON
 c.table_name = x.table_name AND c.constraint_name = x.constraint_name
 WHERE x.table_name = 'OTHER_MY_TABLE_NAME' AND x.constraint_type = 'R' AND c.column_name ='OTHER_MY_COLUMN_NAME';
 if fName is not null THEN
  execute immediate 'alter table OTHER_MY_TABLE_NAME drop constraint ' || fName;
 end if;
end;

嗨@，我正在使用上面的代码来获取我想要删除的约束的名称，并且我有很多这样的选择，而不是 if -> drop 语句。我的问题是，如果其中一个选择不返回任何内容，则会引发异常。我可以捕捉到异常，但在“开始结束”结构的末尾（所以在所有的选择语句之后，其余的删除将永远不会被执行）。我该如何安排呢，如果选择什么都不返回，我只是不想放弃任何东西:)

如果有另一种方法来定义一个变量并从 select 中填充它而不抛出异常，无论返回的名称是否为 null，我都会更喜欢它 :)（现在我只是让这个 select 工作，除了选择不返回任何内容的情况:))

【问题讨论】：

标签： oracle exception select

【解决方案1】：

使用多个开始/异常/结束块：

declare
 fName varchar2(255 char);
begin
 begin
   SELECT x.constraint_name into fName FROM all_constraints x
   JOIN all_cons_columns c ON
   c.table_name = x.table_name AND c.constraint_name = x.constraint_name
   WHERE x.table_name = 'MY_TABLE_NAME' AND x.constraint_type = 'R' AND c.column_name ='MY_COLUMN_NAME';
exception
  when no_data_found then
    fName := null;
end;

 if fName is not null THEN
  execute immediate 'alter table MY_TABLE_NAME drop constraint ' || fName;
 end if;

begin    
 SELECT x.constraint_name into fName FROM all_constraints x
 JOIN all_cons_columns c ON
 c.table_name = x.table_name AND c.constraint_name = x.constraint_name
 WHERE x.table_name = 'OTHER_MY_TABLE_NAME' AND x.constraint_type = 'R' AND c.column_name ='OTHER_MY_COLUMN_NAME';
exception
  when no_data_found then
    fName := null;
end;

 if fName is not null THEN
  execute immediate 'alter table OTHER_MY_TABLE_NAME drop constraint ' || fName;
 end if;
end;

【讨论】：

【解决方案2】：

使用本地程序：

declare

  procedure drop_constraint(i_table_name in varchar2, i_column_name in varchar2)
  is
    l_constr_name varchar2(255 char);
  begin
    SELECT x.constraint_name into fName FROM all_constraints x
    JOIN all_cons_columns c ON c.table_name = x.table_name AND c.constraint_name = x.constraint_name
    WHERE x.table_name = i_table_name AND x.constraint_type = 'R' AND c.column_name = i_column_name;

    execute immediate 'alter table ' || i_table_name || ' drop constraint ' || l_constr_name;

  exception
    when NO_DATA_FOUND then
      null; -- ignore or print message
  end drop_constraint;

begin
   drop_constraint('MY_TABLE_NAME', 'MY_COLUMN_NAME');
   drop_constraint('OTHER_TABLE_NAME', 'OTHER_COLUMN_NAME');
end;
/

【讨论】：