Index: trunk/ippTools/share/difftool_definebyquery.sql
===================================================================
--- trunk/ippTools/share/difftool_definebyquery.sql	(revision 18656)
+++ trunk/ippTools/share/difftool_definebyquery.sql	(revision 18656)
@@ -0,0 +1,58 @@
+-- Get list of warps that can be diffed, with any associated diff,
+-- and the best stack to use as a template
+-- Warps without an existing diff can be identified by a NULL diff_id
+SELECT
+    warpsToDiff.warp_id,
+    warpsToDiff.skycell_id,
+    warpsToDiff.tess_id,
+    warpsToDiff.filter,
+    warpsToDiff.diff_id,
+    warpsToDiff.kind,
+    current_stack_id,
+    best_stack_id
+FROM (
+    -- Get list of warps that can be diffed, with any associated diff
+    SELECT
+        warpSkyfile.warp_id,
+        warpSkyfile.skycell_id,
+        warpSkyfile.tess_id,
+        filter,
+        diffInputs.diff_id,
+        diffInputs.kind,
+        diffTemplates.stack_id AS current_stack_id
+    FROM warpSkyfile
+    JOIN warpRun USING(warp_id, tess_id)
+    JOIN fakeRun USING(fake_id, tess_id)
+    JOIN camRun USING(cam_id, tess_id)
+    JOIN chipRun USING(chip_id, tess_id)
+    JOIN rawExp USING(exp_id, tess_id)
+    -- Check if it has an associated diff
+    LEFT JOIN diffInputSkyfile AS diffInputs
+        ON diffInputs.warp_id = warpSkyfile.warp_id
+        AND diffInputs.skycell_id = warpSkyfile.skycell_id
+        AND diffInputs.tess_id = warpSkyfile.tess_id
+        AND diffInputs.template = 0 -- only join input files
+    -- Get the stack_id currently used as a template, if any
+    LEFT JOIN diffInputSkyfile AS diffTemplates
+        ON diffTemplates.diff_id = diffInputs.diff_id
+        AND diffTemplates.template != 0 -- only join template files
+    WHERE
+        warpSkyfile.fault = 0
+        AND warpSkyfile.ignored = 0
+    ) AS warpsToDiff
+-- Get best stack as a function of skycell_id, filter
+JOIN (
+    SELECT
+        MAX(stack_id) AS best_stack_id, -- most recent stack, by virtue of auto-increment
+        skycell_id,
+        tess_id,
+        filter
+    FROM stackRun
+    JOIN stackSumSkyfile USING(stack_id)
+    WHERE stackRun.state = 'stop'
+        AND stackSumSkyfile.fault = 0
+    GROUP BY
+        skycell_id,
+        tess_id,
+        filter
+    ) AS stacksForDiff USING(skycell_id, tess_id, filter)