If the LHS for an EXCEPT or INTERSECT operator is empty, skip over the

computation of the RHS.

FossilOrigin-Name: 13f096ae8a850a05d4a8684561066f11693ee66289e6568c44ef32822cca06f6

src/vdbe.c

@@ -6398,6 +6398,31 @@ case OP_Rewind: {        /* jump0, ncycle */
   break;
 }
 
+/* Opcode: IfEmpty P1 P2 * * *
+** Synopsis: if( empty(P1) ) goto P2
+**
+** Check to see if the b-tree table that cursor P1 references is empty
+** and jump to P2 if it is.
+*/
+case OP_IfEmpty: {        /* jump */
+  VdbeCursor *pC;
+  BtCursor *pCrsr;
+  int res;
+
+  assert( pOp->p1>=0 && pOp->p1<p->nCursor );
+  assert( pOp->p2>=0 && pOp->p2<p->nOp );
+
+  pC = p->apCsr[pOp->p1];
+  assert( pC!=0 );
+  assert( pC->eCurType==CURTYPE_BTREE );
+  pCrsr = pC->uc.pCursor;
+  assert( pCrsr );
+  res = sqlite3BtreeIsEmpty(pCrsr);
+  VdbeBranchTaken(res!=0,2);
+  if( res ) goto jump_to_p2;
+  break;
+}
+
 /* Opcode: Next P1 P2 P3 * P5
 **
 ** Advance cursor P1 so that it points to the next key/data pair in its