SQL 根据传递的参数查询

Question

I have a condition, where if the parameter passed is US then I want the input_value to be "Hours Calculated", if it is CA then I want it to be "HRS" and "Hours" and if I do not pass anything then all three should be picked.

Select element_name
from element_tab JOIN
INPUTVAL_TAB
where ELEMENT_TAB.LEGISLATION_CODE = nvl(:P_LC,ELEMENT_TAB.LEGISLATION_CODE)
AND INPUTVAL_TAB.INPUT_ID = ELEMENT_TAB.INPUT_ID
AND INPUTVAL_TAB.BASE_NAME = DECODE(:p_LC,'US','Hours Calculated','CA','HRS','CA','Hours')

How can the above query be changed so that if i do not pass:p_LC parameter then 'Hours Calculated','HRS' and 'Hours', all three are picked?

Answer 1

You can check for a null value:

AND (
     (:p_LC IS NULL
      AND INPUTVAL_TAB.BASE_NAME IN ('Hours Calculated', 'HRS', 'Hours'))
  OR (:p_LC IS NOT NULL
      AND INPUTVAL_TAB.BASE_NAME = DECODE(:p_LC,'US','Hours Calculated','CA','HRS','CA','Hours'))
)

It might be clearer, for someone maintaining this in the future, to do:

AND (
     (:p_LC IS NULL AND INPUTVAL_TAB.BASE_NAME IN ('Hours Calculated', 'HRS', 'Hours'))
  OR (:p_LC = 'US' AND INPUTVAL_TAB.BASE_NAME = 'Hours Calculated')
  OR (:p_LC = 'CA' AND INPUTVAL_TAB.BASE_NAME IN ('HRS', 'Hours'))
)

---

I have already used NVL to check the:p_lc null value

Not relevant, but personally'd I'd prefer to do the first check the same way; so rather than:

where ELEMENT_TAB.LEGISLATION_CODE = nvl(:P_LC,ELEMENT_TAB.LEGISLATION_CODE)

I would do:

where (
  :p_LC IS NULL
  OR ELEMENT_TAB.LEGISLATION_CODE = :p_LC
)

... but that's largely a matter of taste.