Question

I have a somewhat complex mySQL query I am trying to execute. I have two parameters: facility and isEnabled. Facility can have a value of “ALL” or be specific ID. isEnabled can have value of “ALL” or be 0/1.

My issue is that I need to come up with logic that can handle the following scenarios:
1) Facility = ALL AND isEnabled = ALL
2) Facility = ALL AND isEnabled = value
3) Facility = someID AND isEnabled = ALL
4) Facility = someID AND isEnabled = value

The problem is that I have several nested IF statements:

IF (Facility = 'ALL') THEN
  IF (isEnabled = 'ALL') THEN
    SELECT * FROM myTable
  ELSE
    SELECT * FROM myTable
    WHERE isEnabled = value
  END IF;
ELSE
  IF (isEnabled = 'ALL') THEN
    SELECT * FROM myTable
    WHERE facility = someID
  ELSE
    SELECT * FROM myTable
    WHERE facility = someID AND isEnabled = value
  END IF;
END IF;

I would like to be able to combine the logic in the WHERE clause using either a CASE statement or Conditional’s (AND/OR) but I am having trouble wrapping my head around it this morning. Currently the query is not performing as it is expected to be.

Any insight would be helpful!
Thanks

Answer 1

You could do this…

SELECT
  *
FROM
  myTable
WHERE
  1=1
  AND (facility  = someID OR Facility  = 'ALL')
  AND (isEnabled = value  OR isEnabled = 'ALL')

However, this yields a poor execution plan – it’s trying to find one size fits all, but each combination of parameters can have different plans depending on data, indexes, etc.

This means that it is better to build the query dynamically

SELECT
  *
FROM
  myTable
WHERE
  1=1
  AND facility  = someID  -- Only include this line if : Facility  = 'ALL'
  AND isEnabled = value   -- Only include this line if : isEnabled = 'ALL'

I know it can feel dirty to use dynamic queries, but this is a good corner case as to when then really can excel. I’ll go find a spectacularly informative link for you now. (It’s a lot to read, but it’s very worth learning from)

Link : Dynamic Search