Is it possible to integrate some conditionals in a SELECT query? Here's my current working query:

Code:
SELECT f.fieldID, f.fieldNew, f.fieldFeatured, f.fieldSale, f.fieldTitle,
	f.fieldDrillGrade, TRUNCATE(ROUND(AVG(i.itemGrade) * 2) / 2,1) AS fieldMusicGradeAvg,
	g.genreName, (f.fieldSets1 + f.fieldSets2 + f.fieldSets3 + f.fieldSets4 + f.fieldSets5) AS fieldTotalSets,
	SUM(i.itemTime) AS fieldTotalTime, SUM(i.itemPrice) + f.fieldDrillOnly AS fieldTotalPrice 
FROM field AS f 
INNER JOIN items AS i ON i.itemID IN (f.fieldMusic1, f.fieldMusic2, f.fieldMusic3, f.fieldMusic4, f.fieldMusic5) 
LEFT OUTER JOIN genres AS g ON g.genreID = f.fieldGenre 
WHERE f.fieldEnabled = 'Yes' 
GROUP BY f.fieldTitle, f.fieldDrillGrade
ORDER BY f.fieldTitle
Here's what I need to accomplish now:

Some records in the "field" table may NOT be associated with records in the "items" table. If fieldMusicTitle1, fieldMusicTitle2, fieldMusicTitle3, fieldMusicTitle4, or fieldMusicTitle5 (new fields) have content -- I need the query to IGNORE the INNER JOIN with the items table.

If this conditional is true -- I also need:

* fieldMusicGradeAvg would then become the value of fieldMusicGrade (new field).

* fieldTotalTime would then become the sum of fieldTime1, fieldTime2, fieldTime3, fieldTime4, fieldTime5 (new fields).

* fieldTotalPrice would then become the sum of fieldMusicOnly and fieldDrillOnly.

Is this all even possible? Thank you for any help you can provide.