}
  return 0;
}

/*
** This is the Expr node callback for sqlite3ExprImpliesNotNullRow().
** If the expression node requires that the table at pWalker->iCur
** have a non-NULL column, then set pWalker->eCode to 1 and abort.
*/
static int impliesNotNullRow(Walker *pWalker, Expr *pExpr){
  /* This routine is only called for WHERE clause expressions and so it
  ** cannot have any TK_AGG_COLUMN entries because those are only found
  ** in HAVING clauses.  We can get a TK_AGG_FUNCTION in a WHERE clause,
  ** but that is an illegal construct and the query will be rejected at
  ** a later stage of processing, so the TK_AGG_FUNCTION case does not
  ** need to be considered here. */
  assert( pExpr->op!=TK_AGG_COLUMN );
  testcase( pExpr->op==TK_AGG_FUNCTION );

  if( ExprHasProperty(pExpr, EP_FromJoin) ) return WRC_Prune;
  switch( pExpr->op ){
    case TK_ISNOT:
    case TK_NOT:
    case TK_ISNULL:
    case TK_IS:
    case TK_OR:

  }
  return 0;
}

/*
** This is the Expr node callback for sqlite3ExprImpliesNotNullRow().
** If the expression node requires that the table at pWalker->iCur
** have one or more non-NULL column, then set pWalker->eCode to 1 and abort.
**
** This routine controls an optimization.  False positives (setting
** pWalker->eCode to 1 when it should not be) are deadly, but false-negatives
** (never setting pWalker->eCode) is a harmless missed optimization.
*/
static int impliesNotNullRow(Walker *pWalker, Expr *pExpr){
  testcase( pExpr->op==TK_AGG_COLUMN );
  testcase( pExpr->op==TK_AGG_FUNCTION );



  if( ExprHasProperty(pExpr, EP_FromJoin) ) return WRC_Prune;
  switch( pExpr->op ){
    case TK_ISNOT:
    case TK_NOT:
    case TK_ISNULL:
    case TK_IS:
    case TK_OR: