if( pSrc->a[0].pSelect ) return 0;     /* FROM is not a subquery or view */
  pTab = pSrc->a[0].pTab;
  assert( pTab!=0 );
  assert( pTab->pSelect==0 );            /* FROM clause is not a view */
  if( IsVirtual(pTab) ) return 0;        /* FROM clause not a virtual table */
  pEList = p->pEList;
  assert( pEList!=0 );

  /* All SELECT results must be columns. */
  for(i=0; i<pEList->nExpr; i++){
    Expr *pRes = pEList->a[i].pExpr;
    if( pRes->op!=TK_COLUMN ) return 0;
    assert( pRes->iTable==pSrc->a[0].iCursor );  /* Not a correlated subquery */
  }
  return p;
................................................................................
    pTab = p->pSrc->a[0].pTab;

    /* Code an OP_Transaction and OP_TableLock for <table>. */
    iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
    sqlite3CodeVerifySchema(pParse, iDb);
    sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);

    /* This function is only called from two places. In both cases the vdbe
    ** has already been allocated. So assume sqlite3GetVdbe() is always
    ** successful here.
    */
    assert(v);
    if( nExpr==1 && pEList->a[0].pExpr->iColumn<0 ){
      /* The "x IN (SELECT rowid FROM table)" case */
      int iAddr = sqlite3CodeOnce(pParse);
      VdbeCoverage(v);

      sqlite3OpenTable(pParse, iTab, iDb, pTab, OP_OpenRead);
      eType = IN_INDEX_ROWID;
................................................................................
            assert( idxaff==SQLITE_AFF_TEXT );
            break;
          default:
            affinity_ok = sqlite3IsNumericAffinity(idxaff);
        }
      }

      /* The collation sequence used by the comparison. If an index is to
      ** be used in place of a temp-table, it must be ordered according
      ** to this collation sequence.  */

      for(pIdx=pTab->pIndex; pIdx && eType==0 && affinity_ok; pIdx=pIdx->pNext){


        if( pIdx->nColumn<nExpr ) continue;





        if( mustBeUnique ){
          if( pIdx->nKeyCol>nExpr
           ||(pIdx->nColumn>nExpr && !IsUniqueIndex(pIdx))
          ){
            continue;

          }
        }


        for(i=0; i<nExpr; i++){
          Expr *pLhs = sqlite3VectorFieldSubexpr(pX->pLeft, i);
          Expr *pRhs = pEList->a[i].pExpr;
          CollSeq *pReq = sqlite3BinaryCompareCollSeq(pParse, pLhs, pRhs);
          int j;

          assert( pReq!=0 || pRhs->iColumn==XN_ROWID || pParse->nErr );
          for(j=0; j<nExpr; j++){
            if( pIdx->aiColumn[j]!=pRhs->iColumn ) continue;
            assert( pIdx->azColl[j] );
            if( pReq==0 ) continue;
            if( sqlite3StrICmp(pReq->zName, pIdx->azColl[j])!=0 ) continue;
            break;
          }
          if( j==nExpr ) break;



          if( aiMap ) aiMap[i] = j;
        }

        if( i==nExpr ){



          int iAddr = sqlite3CodeOnce(pParse); VdbeCoverage(v);
#ifndef SQLITE_OMIT_EXPLAIN
          sqlite3VdbeAddOp4(v, OP_Explain, 0, 0, 0,
            sqlite3MPrintf(db, "USING INDEX %s FOR IN-OPERATOR", pIdx->zName),
            P4_DYNAMIC);
#endif
          sqlite3VdbeAddOp3(v, OP_OpenRead, iTab, pIdx->tnum, iDb);
          sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
          VdbeComment((v, "%s", pIdx->zName));
          assert( IN_INDEX_INDEX_DESC == IN_INDEX_INDEX_ASC+1 );
          eType = IN_INDEX_INDEX_ASC + pIdx->aSortOrder[0];

          if( prRhsHasNull ){
            *prRhsHasNull = ++pParse->nMem;
#ifdef SQLITE_ENABLE_COLUMN_USED_MASK
            i64 mask = (1<<nExpr)-1;
            sqlite3VdbeAddOp4Dup8(v, OP_ColumnsUsed, 
                iTab, 0, 0, (u8*)&mask, P4_INT64);
#endif
            if( nExpr==1 ){
              sqlite3SetHasNullFlag(v, iTab, *prRhsHasNull);
            }
          }
          sqlite3VdbeJumpHere(v, iAddr);
        }
      }
    }
  }





  /* If no preexisting index is available for the IN clause
  ** and IN_INDEX_NOOP is an allowed reply
  ** and the RHS of the IN operator is a list, not a subquery
  ** and the RHS is not constant or has two or fewer terms,
  ** then it is not worth creating an ephemeral table to evaluate
  ** the IN operator so return IN_INDEX_NOOP.

  if( pSrc->a[0].pSelect ) return 0;     /* FROM is not a subquery or view */
  pTab = pSrc->a[0].pTab;
  assert( pTab!=0 );
  assert( pTab->pSelect==0 );            /* FROM clause is not a view */
  if( IsVirtual(pTab) ) return 0;        /* FROM clause not a virtual table */
  pEList = p->pEList;
  assert( pEList!=0 );

  /* All SELECT results must be columns. */
  for(i=0; i<pEList->nExpr; i++){
    Expr *pRes = pEList->a[i].pExpr;
    if( pRes->op!=TK_COLUMN ) return 0;
    assert( pRes->iTable==pSrc->a[0].iCursor );  /* Not a correlated subquery */
  }
  return p;
................................................................................
    pTab = p->pSrc->a[0].pTab;

    /* Code an OP_Transaction and OP_TableLock for <table>. */
    iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
    sqlite3CodeVerifySchema(pParse, iDb);
    sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);

    assert(v);  /* sqlite3GetVdbe() has always been previously called */




    if( nExpr==1 && pEList->a[0].pExpr->iColumn<0 ){
      /* The "x IN (SELECT rowid FROM table)" case */
      int iAddr = sqlite3CodeOnce(pParse);
      VdbeCoverage(v);

      sqlite3OpenTable(pParse, iTab, iDb, pTab, OP_OpenRead);
      eType = IN_INDEX_ROWID;
................................................................................
            assert( idxaff==SQLITE_AFF_TEXT );
            break;
          default:
            affinity_ok = sqlite3IsNumericAffinity(idxaff);
        }
      }

      if( affinity_ok ){
        /* Search for an existing index that will work for this IN operator */


        for(pIdx=pTab->pIndex; pIdx && eType==0; pIdx=pIdx->pNext){
          Bitmask colUsed;      /* Columns of the index used */
          Bitmask mCol;         /* Mask for the current column */
          if( pIdx->nColumn<nExpr ) continue;
          /* Maximum nColumn is BMS-2, not BMS-1, so that we can compute
          ** BITMASK(nExpr) without overflowing */
          testcase( pIdx->nColumn==BMS-2 );
          testcase( pIdx->nColumn==BMS-1 );
          if( pIdx->nColumn>=BMS-1 ) continue;
          if( mustBeUnique ){
            if( pIdx->nKeyCol>nExpr
             ||(pIdx->nColumn>nExpr && !IsUniqueIndex(pIdx))
            ){

              continue;  /* This index is not unique over the IN RHS columns */
            }
          }
  
          colUsed = 0;   /* Columns of index used so far */
          for(i=0; i<nExpr; i++){
            Expr *pLhs = sqlite3VectorFieldSubexpr(pX->pLeft, i);
            Expr *pRhs = pEList->a[i].pExpr;
            CollSeq *pReq = sqlite3BinaryCompareCollSeq(pParse, pLhs, pRhs);
            int j;
  
            assert( pReq!=0 || pRhs->iColumn==XN_ROWID || pParse->nErr );
            for(j=0; j<nExpr; j++){
              if( pIdx->aiColumn[j]!=pRhs->iColumn ) continue;
              assert( pIdx->azColl[j] );
              if( pReq==0 ) continue;
              if( sqlite3StrICmp(pReq->zName, pIdx->azColl[j])!=0 ) continue;
              break;
            }
            if( j==nExpr ) break;
            mCol = MASKBIT(j);
            if( mCol & colUsed ) break; /* Each column used only once */
            colUsed |= mCol;
            if( aiMap ) aiMap[i] = j;
          }
  

          assert( i==nExpr || colUsed!=(MASKBIT(nExpr)-1) );
          if( colUsed==(MASKBIT(nExpr)-1) ){
            /* If we reach this point, that means the index pIdx is usable */
            int iAddr = sqlite3CodeOnce(pParse); VdbeCoverage(v);
  #ifndef SQLITE_OMIT_EXPLAIN
            sqlite3VdbeAddOp4(v, OP_Explain, 0, 0, 0,
              sqlite3MPrintf(db, "USING INDEX %s FOR IN-OPERATOR",pIdx->zName),
              P4_DYNAMIC);
  #endif
            sqlite3VdbeAddOp3(v, OP_OpenRead, iTab, pIdx->tnum, iDb);
            sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
            VdbeComment((v, "%s", pIdx->zName));
            assert( IN_INDEX_INDEX_DESC == IN_INDEX_INDEX_ASC+1 );
            eType = IN_INDEX_INDEX_ASC + pIdx->aSortOrder[0];
  
            if( prRhsHasNull ){
              *prRhsHasNull = ++pParse->nMem;
  #ifdef SQLITE_ENABLE_COLUMN_USED_MASK
              i64 mask = (1<<nExpr)-1;
              sqlite3VdbeAddOp4Dup8(v, OP_ColumnsUsed, 
                  iTab, 0, 0, (u8*)&mask, P4_INT64);
  #endif
              if( nExpr==1 ){
                sqlite3SetHasNullFlag(v, iTab, *prRhsHasNull);
              }
            }
            sqlite3VdbeJumpHere(v, iAddr);
          }



        } /* End loop over indexes */
      } /* End if( affinity_ok ) */
    } /* End if not an rowid index */
  } /* End attempt to optimize using an index */

  /* If no preexisting index is available for the IN clause
  ** and IN_INDEX_NOOP is an allowed reply
  ** and the RHS of the IN operator is a list, not a subquery
  ** and the RHS is not constant or has two or fewer terms,
  ** then it is not worth creating an ephemeral table to evaluate
  ** the IN operator so return IN_INDEX_NOOP.