Index: src/where.c
==================================================================
--- src/where.c
+++ src/where.c
@@ -271,15 +271,16 @@
   int j;
 
   /* memset(pScan, 0, sizeof(*pScan)); */
   pScan->pOrigWC = pWC;
   pScan->pWC = pWC;
+  if( pIdx ){
+    j = iColumn;
+    iColumn = pIdx->aiColumn[j];
+  }
   if( pIdx && iColumn>=0 ){
     pScan->idxaff = pIdx->pTable->aCol[iColumn].affinity;
-    for(j=0; pIdx->aiColumn[j]!=iColumn; j++){
-      if( NEVER(j>pIdx->nColumn) ) return 0;
-    }
     pScan->zCollName = pIdx->azColl[j];
   }else{
     pScan->idxaff = 0;
     pScan->zCollName = 0;
   }
@@ -295,10 +296,13 @@
 /*
 ** Search for a term in the WHERE clause that is of the form "X <op> <expr>"
 ** where X is a reference to the iColumn of table iCur and <op> is one of
 ** the WO_xx operator codes specified by the op parameter.
 ** Return a pointer to the term.  Return 0 if not found.
+**
+** If pIdx!=0 then search for terms matching the iColumn-th column of pIdx
+** rather than the iColumn-th column of table iCur.
 **
 ** The term returned might by Y=<expr> if there is another constraint in
 ** the WHERE clause that specifies that X=Y.  Any such constraints will be
 ** identified by the WO_EQUIV bit in the pTerm->eOperator field.  The
 ** aEquiv[] array holds X and all its equivalents, with each SQL variable
@@ -372,10 +376,28 @@
     }
   }
 
   return -1;
 }
+
+/*
+** Return TRUE if the iCol-th column of index pIdx is NOT NULL
+*/
+static int indexColumnNotNull(Index *pIdx, int iCol){
+  int j;
+  assert( pIdx!=0 );
+  assert( iCol>=0 && iCol<pIdx->nColumn );
+  j = pIdx->aiColumn[iCol];
+  if( j>=0 ){
+    return pIdx->pTable->aCol[j].notNull;
+  }else if( j==(-1) ){
+    return 1;
+  }else{
+    assert( j==(-2) );
+    return !sqlite3ExprCanBeNull(pIdx->aColExpr->a[iCol].pExpr);
+  }
+}
 
 /*
 ** Return true if the DISTINCT expression-list passed as the third argument
 ** is redundant.
 **
@@ -423,16 +445,13 @@
   **      contain a "col=X" term are subject to a NOT NULL constraint.
   */
   for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
     if( !IsUniqueIndex(pIdx) ) continue;
     for(i=0; i<pIdx->nKeyCol; i++){
-      i16 iCol = pIdx->aiColumn[i];
-      if( 0==sqlite3WhereFindTerm(pWC, iBase, iCol, ~(Bitmask)0, WO_EQ, pIdx) ){
-        int iIdxCol = findIndexCol(pParse, pDistinct, iBase, pIdx, i);
-        if( iIdxCol<0 || pTab->aCol[iCol].notNull==0 ){
-          break;
-        }
+      if( 0==sqlite3WhereFindTerm(pWC, iBase, i, ~(Bitmask)0, WO_EQ, pIdx) ){
+        if( findIndexCol(pParse, pDistinct, iBase, pIdx, i)<0 ) break;
+        if( indexColumnNotNull(pIdx, i)==0 ) break;
       }
     }
     if( i==pIdx->nKeyCol ){
       /* This index implies that the DISTINCT qualifier is redundant. */
       return 1;
@@ -2124,11 +2143,10 @@
   u16 saved_nLTerm;               /* Original value of pNew->nLTerm */
   u16 saved_nEq;                  /* Original value of pNew->u.btree.nEq */
   u16 saved_nSkip;                /* Original value of pNew->nSkip */
   u32 saved_wsFlags;              /* Original value of pNew->wsFlags */
   LogEst saved_nOut;              /* Original value of pNew->nOut */
-  int iCol;                       /* Index of the column in the table */
   int rc = SQLITE_OK;             /* Return code */
   LogEst rSize;                   /* Number of rows in the table */
   LogEst rLogSize;                /* Logarithm of table size */
   WhereTerm *pTop = 0, *pBtm = 0; /* Top and bottom range constraints */
 
@@ -2145,20 +2163,19 @@
     opMask = WO_EQ|WO_IN|WO_GT|WO_GE|WO_LT|WO_LE|WO_ISNULL|WO_IS;
   }
   if( pProbe->bUnordered ) opMask &= ~(WO_GT|WO_GE|WO_LT|WO_LE);
 
   assert( pNew->u.btree.nEq<pProbe->nColumn );
-  iCol = pProbe->aiColumn[pNew->u.btree.nEq];
 
-  pTerm = whereScanInit(&scan, pBuilder->pWC, pSrc->iCursor, iCol,
-                        opMask, pProbe);
   saved_nEq = pNew->u.btree.nEq;
   saved_nSkip = pNew->nSkip;
   saved_nLTerm = pNew->nLTerm;
   saved_wsFlags = pNew->wsFlags;
   saved_prereq = pNew->prereq;
   saved_nOut = pNew->nOut;
+  pTerm = whereScanInit(&scan, pBuilder->pWC, pSrc->iCursor, saved_nEq,
+                        opMask, pProbe);
   pNew->rSetup = 0;
   rSize = pProbe->aiRowLogEst[0];
   rLogSize = estLog(rSize);
   for(; rc==SQLITE_OK && pTerm!=0; pTerm = whereScanNext(&scan)){
     u16 eOp = pTerm->eOperator;   /* Shorthand for pTerm->eOperator */
@@ -2167,11 +2184,11 @@
     int nIn = 0;
 #ifdef SQLITE_ENABLE_STAT3_OR_STAT4
     int nRecValid = pBuilder->nRecValid;
 #endif
     if( (eOp==WO_ISNULL || (pTerm->wtFlags&TERM_VNULL)!=0)
-     && (iCol<0 || pSrc->pTab->aCol[iCol].notNull)
+     && indexColumnNotNull(pProbe, saved_nEq)
     ){
       continue; /* ignore IS [NOT] NULL constraints on NOT NULL columns */
     }
     if( pTerm->prereqRight & pNew->maskSelf ) continue;
 
@@ -2204,12 +2221,14 @@
       }
       assert( nIn>0 );  /* RHS always has 2 or more terms...  The parser
                         ** changes "x IN (?)" into "x=?". */
 
     }else if( eOp & (WO_EQ|WO_IS) ){
+      int iCol = pProbe->aiColumn[saved_nEq];
       pNew->wsFlags |= WHERE_COLUMN_EQ;
-      if( iCol<0 || (nInMul==0 && pNew->u.btree.nEq==pProbe->nKeyCol-1) ){
+      assert( saved_nEq==pNew->u.btree.nEq );
+      if( iCol==(-1) || (nInMul==0 && saved_nEq==pProbe->nKeyCol-1) ){
         if( iCol>=0 && pProbe->uniqNotNull==0 ){
           pNew->wsFlags |= WHERE_UNQ_WANTED;
         }else{
           pNew->wsFlags |= WHERE_ONEROW;
         }
@@ -2256,11 +2275,11 @@
     }else{
       int nEq = ++pNew->u.btree.nEq;
       assert( eOp & (WO_ISNULL|WO_EQ|WO_IN|WO_IS) );
 
       assert( pNew->nOut==saved_nOut );
-      if( pTerm->truthProb<=0 && iCol>=0 ){
+      if( pTerm->truthProb<=0 && pProbe->aiColumn[saved_nEq]>=0 ){
         assert( (eOp & WO_IN) || nIn==0 );
         testcase( eOp & WO_IN );
         pNew->nOut += pTerm->truthProb;
         pNew->nOut -= nIn;
       }else{
@@ -3783,11 +3802,11 @@
        || pIdx->pPartIdxWhere!=0 
        || pIdx->nKeyCol>ArraySize(pLoop->aLTermSpace) 
       ) continue;
       opMask = pIdx->uniqNotNull ? (WO_EQ|WO_IS) : WO_EQ;
       for(j=0; j<pIdx->nKeyCol; j++){
-        pTerm = sqlite3WhereFindTerm(pWC, iCur, pIdx->aiColumn[j], 0, opMask, pIdx);
+        pTerm = sqlite3WhereFindTerm(pWC, iCur, j, 0, opMask, pIdx);
         if( pTerm==0 ) break;
         testcase( pTerm->eOperator & WO_IS );
         pLoop->aLTerm[j] = pTerm;
       }
       if( j!=pIdx->nKeyCol ) continue;