使用变量作为子查询执行查询

Question

我有一个这样的查询：

select * from SOURCE
where A = 'a'
and B in (
  select SOMECOLUMN from VERY_LONG_QUERY 
  WHERE SOMECHECK = 'some check'
)

我想将上面的查询转换成这样的语句 PL/SQL：

veryLongQueryVar := 'select SOMECOLUMN from VERY_LONG_QUERY WHERE SOMECHECK = ''some check'' ' 

select * from SOURCE
where A = 'a'
and B in veryLongQueryVar

这怎么可能？

Answer 1

您可以使用WITH clause 实现类似的效果：

with veryLongQueryVar as
 (select SOMECOLUMN from VERY_LONG_QUERY WHERE SOMECHECK = 'some check')
select * from SOURCE
where A = 'a'
 and B in (select SOMECOLUMN from veryLongQueryVar)

您还可以使用SELECT INTO 将很长的查询结果选择为变量（某种类型的表）和use table to pass it into IN。但这会导致两个单独的查询，您似乎想避免这种情况。

Answer 2

这里有一个建议，你可以做什么。

您将长查询中的值存储在一个集合中，并在另一个选择中使用它。

declare
  TYPE my_collection IS TABLE OF SOMECOLUMN%type
      INDEX BY number;
  tab my_collection ;
  rec SOURCE%rowtype;
begin
  select SOMECOLUMN 
  bulk collect into tab 
  from VERY_LONG_QUERY 
  WHERE SOMECHECK = 'some check';


  select * into rec 
    from SOURCE
   where A = 'a'
     and B in (select column_value from table(tab);
end; 

您还可以创建动态 SQL 字符串。

declare
  TYPE cur IS REF CURSOR;
  my_cur   cur;
  veryLongQueryVar  varchar2(32000);
begin
  veryLongQueryVar := 'select SOMECOLUMN from VERY_LONG_QUERY WHERE SOMECHECK = ''some check'' ' 

  veryLongQueryVar  := 'select * from SOURCE
                        where A = ''a''
                        and B in ('||veryLongQueryVar ||')'

  open my_cur for veryLongQueryVar  ;
  ....

end;