SQLite

/* Recompute the colNotIdxed field of the Index.
**
** colNotIdxed is a bitmask that has a 0 bit representing each indexed
** columns that are within the first 63 columns of the table.  The
** high-order bit of colNotIdxed is always 1.  All unindexed columns
** of the table have a 1.
**
** 2019-10-24:  For the purpose of this computation, virtual columns are
** not considered to be covered by the index, even if they are in the
** index, because we do not trust the logic in whereIndexExprTrans() to be
** able to find all instances of a reference to the indexed table column
** and convert them into references to the index.  Hence we always want
** the actual table at hand in order to recompute the virtual column, if
** necessary.
**
** The colNotIdxed mask is AND-ed with the SrcList.a[].colUsed mask
** to determine if the index is covering index.
*/
static void recomputeColumnsNotIndexed(Index *pIdx){
  Bitmask m = 0;
  int j;
  Table *pTab = pIdx->pTable;
  for(j=pIdx->nColumn-1; j>=0; j--){
    int x = pIdx->aiColumn[j];
    if( x>=0 && (pTab->aCol[x].colFlags & COLFLAG_VIRTUAL)==0 ){
      testcase( x==BMS-1 );
      testcase( x==BMS-2 );
      if( x<BMS-1 ) m |= MASKBIT(x);
    }
  }
  pIdx->colNotIdxed = ~m;
  assert( (pIdx->colNotIdxed>>63)==1 );

      pIndex->aiColumn[i] = XN_EXPR;
      pIndex->uniqNotNull = 0;
    }else{
      j = pCExpr->iColumn;
      assert( j<=0x7fff );
      if( j<0 ){
        j = pTab->iPKey;
      }else{
        if( pTab->aCol[j].notNull==0 ){
          pIndex->uniqNotNull = 0;
        }
        if( pTab->aCol[j].colFlags & COLFLAG_VIRTUAL ){
          pIndex->bHasVCol = 1;
        }
      }
      pIndex->aiColumn[i] = (i16)j;
    }
    zColl = 0;
    if( pListItem->pExpr->op==TK_COLLATE ){
      int nColl;
      zColl = pListItem->pExpr->u.zToken;

  unsigned uniqNotNull:1;  /* True if UNIQUE and NOT NULL for all columns */
  unsigned isResized:1;    /* True if resizeIndexObject() has been called */
  unsigned isCovering:1;   /* True if this is a covering index */
  unsigned noSkipScan:1;   /* Do not try to use skip-scan if true */
  unsigned hasStat1:1;     /* aiRowLogEst values come from sqlite_stat1 */
  unsigned bNoQuery:1;     /* Do not use this index to optimize queries */
  unsigned bAscKeyBug:1;   /* True if the bba7b69f9849b5bf bug applies */
  unsigned bHasVCol:1;     /* Index references one or more VIRTUAL columns */
#ifdef SQLITE_ENABLE_STAT4
  int nSample;             /* Number of elements in aSample[] */
  int nSampleCol;          /* Size of IndexSample.anEq[] and so on */
  tRowcnt *aAvgEq;         /* Average nEq values for keys not in aSample */
  IndexSample *aSample;    /* Samples of the left-most key */
  tRowcnt *aiRowEst;       /* Non-logarithmic stat1 data for this index */
  tRowcnt nRowEst0;        /* Non-logarithmic number of rows in the index */

** down through the Walker.
*/
typedef struct IdxExprTrans {
  Expr *pIdxExpr;    /* The index expression */
  int iTabCur;       /* The cursor of the corresponding table */
  int iIdxCur;       /* The cursor for the index */
  int iIdxCol;       /* The column for the index */
  int iTabCol;       /* The column for the table */
} IdxExprTrans;

/* The walker node callback used to transform matching expressions into
** a reference to an index column for an index on an expression.
**
** If pExpr matches, then transform it into a reference to the index column
** that contains the value of pExpr.

    pExpr->y.pTab = 0;
    return WRC_Prune;
  }else{
    return WRC_Continue;
  }
}

#ifndef SQLITE_OMIT_GENERATED_COLUMNS
/* A walker node callback that translates a column reference to a table
** into a corresponding column reference of an index.
*/
static int whereIndexExprTransColumn(Walker *p, Expr *pExpr){
  if( pExpr->op==TK_COLUMN ){
    IdxExprTrans *pX = p->u.pIdxTrans;
    if( pExpr->iTable==pX->iTabCur && pExpr->iColumn==pX->iTabCol ){
      pExpr->iTable = pX->iIdxCur;
      pExpr->iColumn = pX->iIdxCol;
    }
  }
  return WRC_Continue;
}
#endif /* SQLITE_OMIT_GENERATED_COLUMNS */

/*
** For an indexes on expression X, locate every instance of expression X
** in pExpr and change that subexpression into a reference to the appropriate
** column of the index.
**
** 2019-10-24: Updated to also translate references to a VIRTUAL column in
** the table into references to the corresponding (stored) column of the
** index.
*/
static void whereIndexExprTrans(
  Index *pIdx,      /* The Index */
  int iTabCur,      /* Cursor of the table that is being indexed */
  int iIdxCur,      /* Cursor of the index itself */
  WhereInfo *pWInfo /* Transform expressions in this WHERE clause */
){
  int iIdxCol;               /* Column number of the index */
  ExprList *aColExpr;        /* Expressions that are indexed */
  Table *pTab;
  Walker w;
  IdxExprTrans x;
  aColExpr = pIdx->aColExpr;
  if( aColExpr==0 && !pIdx->bHasVCol ){
    /* The index does not reference any expressions or virtual columns
    ** so no translations are needed. */
    return;
  }
  pTab = pIdx->pTable;
  memset(&w, 0, sizeof(w));

  w.u.pIdxTrans = &x;
  x.iTabCur = iTabCur;
  x.iIdxCur = iIdxCur;
  for(iIdxCol=0; iIdxCol<pIdx->nColumn; iIdxCol++){
    i16 iRef = pIdx->aiColumn[iIdxCol];
    if( iRef==XN_EXPR ){
      assert( aColExpr->a[iIdxCol].pExpr!=0 );

      x.pIdxExpr = aColExpr->a[iIdxCol].pExpr;
      w.xExprCallback = whereIndexExprTransNode;
#ifndef SQLITE_OMIT_GENERATED_COLUMNS
    }else if( iRef>=0 && (pTab->aCol[iRef].colFlags & COLFLAG_VIRTUAL)!=0 ){
      x.iTabCol = iRef;
      w.xExprCallback = whereIndexExprTransColumn;
#endif /* SQLITE_OMIT_GENERATED_COLUMNS */
    }else{
      continue;
    }
    x.iIdxCol = iIdxCol;
    sqlite3WalkExpr(&w, pWInfo->pWhere);
    sqlite3WalkExprList(&w, pWInfo->pOrderBy);
    sqlite3WalkExprList(&w, pWInfo->pResultSet);
  }
}

/*

      }
      sqlite3VdbeAddOp4Int(v, OP_NotFound, iCur, addrCont,
                           iRowidReg, pPk->nKeyCol); VdbeCoverage(v);
    }

    /* If pIdx is an index on one or more expressions, then look through
    ** all the expressions in pWInfo and try to transform matching expressions
    ** into reference to index columns.  Also attempt to translate references
    ** to virtual columns in the table into references to (stored) columns
    ** of the index.
    **
    ** Do not do this for the RHS of a LEFT JOIN. This is because the 
    ** expression may be evaluated after OP_NullRow has been executed on
    ** the cursor. In this case it is important to do the full evaluation,
    ** as the result of the expression may not be NULL, even if all table
    ** column values are.  https://www.sqlite.org/src/info/7fa8049685b50b5a
    **