I want to output table based on what the user input - sql

Question

User required to input an APP_ID but optional to put MILESTONE_ID and TASK_ID. If MILESTONE_ID only the input, it should be the milestone only not include the task.
Ex. APP_ID: 1 MILESTONE_ID:341 TASK_ID: (blank) = output should be app_id and milestone only.
When APP_ID: 1 MILESTONE_ID: (blank) TASK_ID: 441 = output should be app_id and task only.
Lastly when user input a APP_ID: 1, MILESTONE_ID:341, TASK_ID: 441 = output should be app_id, task and milestone.
My current query is below:
SELECT APPLICATION, MILESTONE_NAME, TASK_NAME, FIELD_NAME, FIELD_ALIAS
FROM TBL_APPLICATIONS A
INNER JOIN TBL_WORKFLOWS B ON B.APPLICATION_FK = A.APPLICATION_PK
INNER JOIN TBL_WORKFLOW_DEFINITION C ON C.WORKFLOW_FK = B.WORKFLOW_PK
INNER JOIN TBL_MILESTONE D ON D.MILESTONE_PK = C.START_MILESTONE_FK OR D.MILESTONE_PK = C.END_MILESTONE_FK
INNER JOIN TBL_TASK_FOR_MILESTONE E ON E.MILESTONE_FK = D.MILESTONE_PK
INNER JOIN TBL_TASK F ON F.TASK_PK = E.TASK_FK strong text
INNER JOIN TBL_REQ_FOR_TASK G ON G.TASK_FK = F.TASK_PK
INNER JOIN TBL_TASK_REQUIREMENTS H ON H.TASK_REQUIREMENT_PK = G.TASK_REQUIREMENT_FK
WHERE APPLICATION_PK = :APPLICATION_ID
OR MILESTONE_PK = :MILESTONE_ID
OR TASK_PK = :TASK_ID
Output looks like this.

Answer 1

Your requirements are slightly unclear. If you want to change the projection of the query or even remove the tables from the FROM clause, that cannot be done in pure SQL. Dynamically assembling queries requires PL/SQL or some other client language.
But if your requirement is simply to conditionally suppress the column value whether a parameter is populated, that can be done by testing each parameter, like this:
SELECT APPLICATION
, case when :MILESTONE_ID is not null then MILESTONE_NAME end as MILESTONE_NAME
, case when :TASK_ID is not null then TASK_NAME end as TASK_NAME
, FIELD_NAME
, FIELD_ALIAS
FROM TBL_APPLICATIONS A
INNER JOIN TBL_WORKFLOWS B ON B.APPLICATION_FK = A.APPLICATION_PK
INNER JOIN TBL_WORKFLOW_DEFINITION C ON C.WORKFLOW_FK = B.WORKFLOW_PK
INNER JOIN TBL_MILESTONE D ON D.MILESTONE_PK = C.START_MILESTONE_FK OR D.MILESTONE_PK = C.END_MILESTONE_FK
INNER JOIN TBL_TASK_FOR_MILESTONE E ON E.MILESTONE_FK = D.MILESTONE_PK
INNER JOIN TBL_TASK F ON F.TASK_PK = E.TASK_FK strong text
INNER JOIN TBL_REQ_FOR_TASK G ON G.TASK_FK = F.TASK_PK
INNER JOIN TBL_TASK_REQUIREMENTS H ON H.TASK_REQUIREMENT_PK = G.TASK_REQUIREMENT_FK
WHERE APPLICATION_PK = :APPLICATION_ID
and ( :MILESTONE_ID is not null or :TASK_ID is not null )
and ( :MILESTONE_ID is null or MILESTONE_PK = :MILESTONE_ID )
and ( :TASK_ID is null or TASK_PK = : )
Note that I have corrected the WHERE clause to include conditions that only filter on MILESTONE_ID or TASK_ID when they are populated.