In the query planner, add a heuristic that will reduce the cost of a full

table scan for a materialized view or subquery if the full scan is the
outer-most loop.  This is shown to speed up some queries.

FossilOrigin-Name: 609fbb94b8f01d6792e5941ab23ce041313d359f6788c4dde6b1ca749ab49137

src/where.c

@@ -3463,6 +3463,9 @@ static int whereLoopAddBtree(
 #else
       pNew->rRun = rSize + 16;
 #endif
+      if( IsView(pTab) || (pTab->tabFlags & TF_Ephemeral)!=0 ){
+        pNew->wsFlags |= WHERE_VIEWSCAN;
+      }
       ApplyCostMultiplier(pNew->rRun, pTab->costMult);
       whereLoopOutputAdjust(pWC, pNew, rSize);
       rc = whereLoopInsert(pBuilder, pNew);
@@ -4843,6 +4846,13 @@ static int wherePathSolver(WhereInfo *pWInfo, LogEst nRowEst){
           rUnsorted -= 2;  /* TUNING:  Slight bias in favor of no-sort plans */
         }
 
+        /* TUNING:  A full-scan of a VIEW or subquery in the outer loop
+        ** is not so bad. */
+        if( iLoop==0 && (pWLoop->wsFlags & WHERE_VIEWSCAN)!=0 ){
+          rCost += -10;
+          nOut += -30;
+        }
+
         /* Check to see if pWLoop should be added to the set of
         ** mxChoice best-so-far paths.
         **

src/whereInt.h

@@ -648,5 +648,6 @@ void sqlite3WhereTabFuncArgs(Parse*, SrcItem*, WhereClause*);
 #define WHERE_BLOOMFILTER  0x00400000  /* Consider using a Bloom-filter */
 #define WHERE_SELFCULL     0x00800000  /* nOut reduced by extra WHERE terms */
 #define WHERE_OMIT_OFFSET  0x01000000  /* Set offset counter to zero */
+#define WHERE_VIEWSCAN     0x02000000  /* A full-scan of a VIEW or subquery */
 
 #endif /* !defined(SQLITE_WHEREINT_H) */