查询前如何声明变量并赋值？

Question

我有一个复杂的查询，必须使用一个称为SubUnitRate的数字。 此变量来自具有特殊条件的另一个表。 简而言之，我们有：

DECLARE
SUBUNITRATE   NUMBER;
BEGIN
SELECT NVL (NULLIF (CU.SUBUNITRATE, 0), 1)
 INTO SUBUNITRATE
 FROM CURRENCYS CU
      JOIN ACCOUNTS ACC ON CU.ID = ACC.CURRENCY
WHERE ACC.ID = :ACCOUNTID;
END;
SELECT SUBUNITRATE * 100 FROM DUAL;

我的目标是获取（在简单情况下）的结果：

SELECT SUBUNITRATE * 100 FROM DUAL;

但是那怎么可能呢？

Answer 1

PL / SQL块不能将查询结果作为查询返回。 相反，您可以打印出结果。

那么，这是您想要的吗？

DECLARE
    SUBUNITRATE   NUMBER;
BEGIN
    SELECT NVL(NULLIF(CU.SUBUNITRATE, 0), 1)
    INTO SUBUNITRATE
    FROM CURRENCYS CU JOIN
         ACC
         ON CU.ID = ACC.CURRENCY
    WHERE ACC.ID = :ACCOUNTID;

    DBMS_OUTPUT.PUT_LINE(SUBUNITRATE * 100)
END;

Answer 2

假设您想在同一查询中多次使用SUBUNITRATE的值，则可以使用WITH子句：

with cte as ( 
   select case 
            when CU.SUBUNITRATE = 0 then 1 
            else CU.SUBUNITRATE 
          end as SUBUNITRATE
   FROM CURRENCYS CU
   JOIN ACCOUNTS ACC ON CU.ID = ACC.CURRENCY
   WHERE ACC.ID = :ACCOUNTID
    )
select cte.SUBUNITRATE * 100
from cte;

Answer 3

无需PL。 APC的简化解决方案，可以直接在查询中使用的形式（无论您说的是... =次单位，还是说= =（从cte中选择sur）-包括括号在内）：

with cte_prelim as (select subunitrate from ... etc.),
cte (sur) as select case when subunit rate is null or subunitrate = 0 then 100
                    else subunitrate * 100 end from cte_prelim)
select...  (your query where you need to use the value)